Problem: No way to check if cascade is in action.

Solution: Add `v:cascading` variable.

Problem:

- annotation-usage-error and code-style-check are disabled.
- vim.inspect relies on a dummy self-assignment for docgen, and its help
  omits parameter and option details.
- LuaLS fallback types obscure iterator inference.
- Docgen hardcodes public function names and appends separately sorted
  files, leaving shared helpers under the inspector heading.

Solution:

- Enable annotation-usage-error and code-style-check, and fix misplaced
  annotations.
- Document vim.inspect's callable module directly, removing the dummy
  assignment. Describe its parameters, option defaults and process
  callback.
- Remove LuaLS iterator fallbacks, correct iterator signatures and check
  values that the improved inference identifies as optional.
- Parse callable modules, require bindings and parent module references.
  Derive public names and inherited function docs from these links,
  including missing help for vim.async.semaphore() and vim.version().
- Export vim.lsp.tagfunc directly with lazy loading and document its
  implementation instead of maintaining a wrapper.
- Group files in section_order, replacing append_only and merge_files.
  Merge declarations before sorting each section, placing shared helpers
  in the main vim section and keeping vim.inspect in alphabetical order.
- Add basic parser coverage for callable modules and module links.

AI-assisted

Enable EmmyLua's need-check-nil diagnostic and resolve nullable values
through more precise types, explicit invariants, and guards for missing
runtime state. Keep analyzer-specific workarounds local and update the
affected API documentation.

Exclude the bundled re.lua from analysis so its nil-check warnings do
not fail CI.

AI-assisted

Problem:
vim.hl.range() computes a segment for every selected line, then discards
all but the outer endpoints for characterwise and linewise highlights.
This makes highlighting large yanks and puts unnecessarily expensive.

Solution:
Use getregionpos() with bounds=true for these highlights. Also use bounds
in the keymap example that only needs the first and last selected lines.

AI-assisted

Problem:
Coordinates-to-position conversion for the finish column in
`vim.hl.range()` checks the start column. This results in an incorrect
finish column when only one of the column coordinates is `vim.v.maxcol`.

Solution:
Check the finish column when converting the finish position. Update the
existing screen test so that a `vim.v.maxcol` finish highlights the
end-of-line marker, matching the existing `-1` behavior.

Other (squashed) commits:

fix(tui): emit ui_send output atomically with the frame

Problem:
tui_ui_send() writes directly to the TTY, bypassing the output buffer.
Sequences sent via nvim_ui_send() (e.g. kitty multiple-cursors, or
visual-dot-repeat) always arrive in a separate TTY write from the frame
they were computed for. This manifests as "tearing", or e.g. in the case
of multicursor the terminal renders text with stale cursor overlays.

Solution:
- tui_ui_send(): while a frame is being assembled (pending invalid
  regions or buffered output), buffer instead of writing directly.
  - Out-of-frame sends (tty queries, clear-on-disable) still write
    immediately.
- mcursor.lua: emit the terminal-cursor update at the end of the redraw
  cycle (`on_end`, when screen positions are final) instead of
  vim.schedule().

Problem:
When `vim.hl.range(0, …, { timeout = N })` is called, the deferred
`range_hl_clear` captures `buf=0`, which resolves to an arbitrary
"current buffer" at timeout. This may cause a stale highlight that never
gets cleared.

Solution:
Resolve `buf=0` explicitly, before `range_hl_clear` captures it.

Problem:
Diagnostic highlight groups were applied by iterating and calling
`vim.hl.range` for each group individually. That resulted in multiple
extmarks with the same priority being created separately, which does not
allow `DiagnosticUnnecessary` and `DiagnosticDeprecated` with matching
options override `Diagnostic*` styling.

Solution:
Pass the list of hl-groups to `vim.hl.range` so they are applied
together in the correct order.