tooling(codemod): instrumented parser + #{ record-migration codemod

[hyperpolymath]

Branch-only tooling for affinescript#218 (do NOT merge into main — the Codemod_hook instrumentation is for the migration sweep only).

lib/codemod_hook.ml records every record-literal LBRACE byte offset; parser.mly ExprRecord productions call Codemod_hook.note; codemod/ exe inserts '#' at exactly those offsets ({->#{, Foo {->Foo #{). Safety: refuses to rewrite unless every recorded offset is really '{'. Hardened to catch per-file parser exceptions so one bad file can't abort the sweep.

Known limitation (recorded on #218): Affinescript.Parse.parse_file hits a pre-existing Match_failure (parse.ml:49) on stdlib + ~95/261 .affine that the 257 AOT harness parses fine — fix that parse-API bug (next) before the stdlib sweep.

Refs #218

[hyperpolymath]

Closing as superseded.

The #{ record-syntax migration epic #218 already landed on main:

• feat!: Rust-like record syntax — bare { = block, records use #{ } (#218; resolves #215 C+D) #222 (merged 2026-05-18) — grammar/lexer/token change + repo migration; per the merged PR body the AST codemod "proved unsound in ambiguous cases and was not used" and "the codemod tooling is intentionally not committed" — a sound convergent codemod (parse-error driven, new grammar only) was used instead, also not committed.
• docs: document Rust-like #{ } record syntax (#218 step 5) #223 — docs for #{
• docs(estate): #229 ledger — record-sigil correction + string ++ (post-ports) #259 — estate ledger update

This PR's body itself states "do NOT merge into main — the Codemod_hook instrumentation is for the migration sweep only." The migration sweep is done; the instrumented-parser tooling has no remaining purpose on main. Issue #218 is CLOSED.

Sibling PR #310 (the application of the codemod's output) is also being closed as superseded by #222.

No salvage — the lib/codemod_hook.ml + codemod/ tree is branch-only by design.