fix(rescript): stop binary .res resources hanging the indexer (#2176)

[DeusData]

A 4.7 MB binary Godot resource (piko_walk_mesh.res) never finished
indexing: .res maps to ReScript, so the resource was parsed as ReScript
source and the definitions pass spun. Three defects, each fixed:

1. Quadratic usage walk (the hang). The ReScript let binding check
   (is_first_named_part_of, shared with Julia, Typst, Elm, PureScript
   and Nickel) climbed from every named leaf with ts_node_parent, which
   descends from the root and scans each level's children. A binary
   file parses into a flat error tree (~170k root children per MB), so
   each climb cost O(root children) and the file O(n^2): 1 MB spent
   46 s in cbm_extract_unified, 4.7 MB never returned. The check now
   climbs the unified walk's own cursor (O(1) per hop), like the other
   occurrence classifiers; the node-based climb stays only for callers
   outside the walk. 1 MB: 46 s -> 0.03 s; 4.7 MB: 2.2 s end to end.

2. Quadratic lexing in error recovery. tree-sitter retries the lexer at
   every byte of an unparseable stretch with every external token
   valid; the ReScript scanner's template-string loop then ran to the
   next backtick/$/backslash/NUL (end of file if none) and discarded
   the result. That cost O(n^2) inside lexing, where the parse budget's
   progress callback never runs, so such files were dropped by the
   5 s CPU budget instead of parsed -- plain text too (100 KB of
   non-ReScript text: 15 s -> 0.18 s). Local scanner patch: skip the
   template branch when NEWLINE is also valid, which only the ERROR
   state allows. Valid files parse to identical trees. Recorded in
   vendored/grammars/MANIFEST.md.

3. Binary content parsed as source. .res is also Godot's binary
   resource format and the Windows compiled-resource format. Following
   the .m/.cls/.frm/.inc/.cfc precedent, cbm_disambiguate_res reads the
   first 4 KB and reports a file holding a NUL byte as unsupported;
   ReScript text never contains one.

Tests (deterministic work counters, no clocks):

• extraction::extract_rescript_let_bindings_use_the_walk_cursor --
  zero root-descending parent hops at 128 and 1024 statements
  (before: 515 / 4099).
• complexity::complexity_rescript_error_recovery_lexing_is_linear --
  lexer bytes pulled through a chunked TSInput, 4 KB vs 8 KB, ratio
  must be linear (before 3.99, after 2.00).
• language::lang_res_binary_resource_unsupported and
  lang_res_rescript_stays_rescript.

Fixes #2176

---

Known leftover (not in this PR): the same root-descending parent climb remains in other is_policy_binding branches (agda, llvm, wolfram, tlaplus, elixir, lisp, …) in extract_usages.c; a generic cursor-ancestor iterator would fix them all.