Problem:
The default 'ruler' is implemented in C instead of the 'statusline' DSL.

Solution:
Replace the C implementation with a default 'rulerformat' expression.
This is a continuation of #1248 and #33036.

Advantages:
- configuration is more discoverable, the default being a useful example
- users and plugins can augment the default
- code reuse and less C code to maintain
- ui2: due to the use of an item group with `minwid`, it can expand
  instead of truncating when the content gets too long, which is
  particularly useful for locales with long translations of Top/Bot/All

Implementation details:
As is the case for 'statusline', when trying to set 'rulerformat' to an
empty string, the default expression is restored instead, mimicking how
previously the default C implementation would have been activated.
Just like before, `:set rulerformat=` and `:set rulerformat&` have the
same effect, and the ruler is disabled with `:set noruler`.

The default expression uses an item group with `%=`, unlike the fallback
in the previous default statusline `%-14.(%l,%c%V%) %P`, because the
total width and how it is configured is immediately clear without
documentation, it is a more useful pattern in general that works when
both sides have flexible width, and it also works for vim, which is
useful for configuration sharing/reuse.

A truncation marker `%<` is added at the end to mimic how at small
screen widths, the scroll percentage would disappear first, so that the
cursor position can remain fully visible.

BREAKING CHANGES:
- `&rulerformat` can no longer be set to an empty string
- ui2: the default ruler is no longer of fixed width, but can expand
- at very small screen widths (< 36 columns)
  - ui2: it will no longer try to shrink white-space before truncating
  - it truncates gradually from the right, whereas previously, the
    scroll percentage would disappear all at once
- l10n can no longer add a space after the comma between line and column
  (this was only done for one language: Ukrainian)

Problem:
The magic globals `it`, `describe`, etc., are more trouble than they are
worth.

- Hooking into `after_each` requires `getfenv()` hacks.
- They confuse luals/emmylua, because the top-level `.luarc.json` isn't
  merged with `test/.luarc.json` (apparently a luals limitation?)
- They totally defeat discoverability because the user just has to
  "know" about the various magic symbols.

So they harm DX, which means they serve no purpose at all.

Solution:
- Expose the test API from `testutil`, so tests can call `t.it()`,
  `t.describe()`, etc., in the conventional way.
- Drop `getfenv()` hacks.
- Drop the `setfenv()` injection in `load_chunk`.
- Drop `test/_meta.lua`.

Problem:
Mysterious Windows CI failure points to resource exhaustion, but we have
no visibility/instrumentation:

    RUN      T610 nvim_set_keymap, nvim_del_keymap can set mappings with special characters, lhs: <S-Left>, rhs: <S-Left>: 93.70 ms OK
    RUN      T611 nvim_set_keymap, nvim_del_keymap can set mappings with special characters, lhs: <S-Left>, rhs: <F12><F2><Tab>: 49.48 ms FAIL
    …\testnvim.lua:144: EOF was received from Nvim. Likely the Nvim process crashed.
    stack traceback:
            D:/a/neovim/neovim/test/functional/testnvim.lua:144: in function 'nvim_set_keymap'
            …/api/keymap_spec.lua:769: in function <…/api/keymap_spec.lua:768>
    RUN      T612 nvim_set_keymap, nvim_del_keymap can set mappings with special characters, lhs: <S-Left>, rhs: <Space><Tab>: 18.49 ms FAIL
    …\testnvim.lua:144: EOF was received from Nvim. Likely the Nvim process crashed.
    stack traceback:
            D:/a/neovim/neovim/test/functional/testnvim.lua:144: in function 'nvim_set_keymap'
            …/api/keymap_spec.lua:769: in function <.../build/Xtest_xdg_api/test/functional/api/keymap_spec.lua:768>

Solution:
Append the child exit-code and signal to the "EOF … crashed" message.

Example:

    Nvim EOF (crash?) exit code: 42 (0x0000002A)

On the next failing Windows run, the first crash line will classify the failure:
- 0xC0000005 → access violation (nvim bug)
- 0xC0000374 → heap corruption (nvim bug)
- spawn/resource error or "clean" exit-code → system resource exhaustion

    FAILED   …/plugin/pack_spec.lua:92: …/plugin/pack_spec.lua @ 70: vim.pack update() can use lockfile revision as a target
    …/plugin/pack_spec.lua:92: …/plugin/pack_spec.lua:70: process still exists
    stack traceback:
    D:/a/neovim/neovim/test/functional/testnvim/exec_lua.lua:124: in function 'system_sync'
    …/plugin/pack_spec.lua:92: in function 'git_cmd'
    …/plugin/pack_spec.lua:113: in function 'git_add_commit'
    …/plugin/pack_spec.lua:1209: in function <…/plugin/pack_spec.lua:1173>

fix #40167

Problem:
unreliable test:

    FAILED   …/tui_spec.lua @ 895: TUI mouse events work with right-click menu (escape sequences sent to child)
    D:/a/…/testnvim.lua:144: Vim:Failed to start server: address already in use
    stack traceback:
    D:/a/…/testnvim.lua:144: in function 'eval'
    D:/a/…/testnvim.lua:1015: in function 'new_pipename'
    …/tui_spec.lua:897: in function <…/tui_spec.lua:895>

Solution:
Workaround potential PID reuse.

Problem:
The Lua test harness still ran through standalone -ll mode, so tests
depended on the low-level Lua path instead of the regular Nvim Lua
environment. That also meant os.exit() coverage had to carry an ASAN
workaround because Lua's raw process exit skipped Nvim teardown and let
LeakSanitizer interfere with the observed exit code.

Solution:
Run the harness and related fixtures with nvim -l. Patch os.exit() in
the main Lua state to exit through getout(), so scripts observe normal
Nvim shutdown while standalone -ll remains available for generator-style
scripts. As a consequence, the startup test can assert os.exit() without
disabling leak detection.

AI-assisted: Codex

Both for tests and for system wide install, $PREFIX/lib/nvim/parser
is a valid path for tree-sitter parsers. This also brings the build.zig
behavior in line with how we set up the paths in CMakeLists.txt

Replace the busted-based Lua test runner with a repo-local harness.

The new harness runs spec files directly under `nvim -ll`, ships its own
reporter and lightweight `luassert` shim, and keeps the helper/preload
flow used by the functional and unit test suites.

Keep the file boundary model shallow and busted-like by restoring `_G`,
`package.loaded`, `package.preload`, `arg`, and the process environment
between files, without carrying extra reset APIs or custom assertion
machinery.

Update the build and test entrypoints to use the new runner, add
black-box coverage for the harness itself, and drop the bundled
busted/luacheck dependency path.

AI-assisted: Codex