Problem:
`parse_ssh_config()` compares tables against a freshly allocated empty
table.
- In `parse_multiple_values()`, the guard which avoids flushing an empty
  accumulator never applies. Runs of separators and trailing whitespace
  push empty strings into the results, and `is_valid()` does not filter
  them. `Host  alpha   beta ` parses as `{ 'alpha', '', 'beta' }`.
- In `parse_value()`, the condition reduces to `chr == '"' and quoted`.
  `quoted` starts false and only that branch sets it, so it can never
  become true: quotes are never recognised and are inserted literally,
  and the unterminated-quote check is unreachable.

Solution:
Compare `#val` instead. Add a test for repeated and trailing separators.

AI-assisted

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`.