perf(javascript): trim walker allocations - #21668

- one-argument fast dispatch for per-identifier hook calls (no rest array
  + spread per identifier)
- closure-free scope entry/exit for the internal block/function scope walks
- guard-branch closures only allocated when a guard frame exists
- inline the Identifier left side of assignments past enterPattern
- pin StackedMap stale-view semantics with unit tests

…21667)

* perf(javascript): own class bodies, methods and object property values

Land class declarations/expressions, class bodies, methods, fields, static
blocks, object methods, shorthand values and property clash checks on
single-shape nodes with the private-name bookkeeping owned, gated back to
acorn on plugin overrides. acorn's share of parse time drops to ~1% on
class- and module-heavy inputs, and many-small-module parsing gets ~4%
faster.

* perf(javascript): stop executing acorn code on the lazy parse path

Own the remaining utility layer — token predicates, scope accessors, error
raising, template-token dispatch, directive prologue, binding-list items,
catch params, the super/class/import atoms and the async/top-level-await
statement heads — as exact copies, so a lazy parse runs entirely in owned
code. A tripwire test instruments acorn's prototype and asserts zero calls;
what remains of the dependency is the class relationship, the token/context
and Unicode tables, and cold fallbacks (using declarations, non-lazy modes,
plugin gates).

* fix(javascript): serialize parse-error locations in the persistent cache

Register a serializer for the parser's ParserPosition so modules carrying a
ModuleParseError stay serializable, restoring the acorn Position behavior
(deserializes to a plain line/column object).

* perf(javascript): trim walker allocations (#21668)

- one-argument fast dispatch for per-identifier hook calls (no rest array
  + spread per identifier)
- closure-free scope entry/exit for the internal block/function scope walks
- guard-branch closures only allocated when a guard frame exists
- inline the Identifier left side of assignments past enterPattern
- pin StackedMap stale-view semantics with unit tests

* chore(changeset): split the lazy-path and walker entry from the parser exactness one

* test(js-parser): cover the public inBlockScope delegate

The walkers now enter and leave block scopes through the closure-free cores, so nothing in the repository executed the plugin-facing inBlockScope any more. Assert its contract: a child definitions scope, reset shorthand state, and termination propagating outward only on an executed path.

* style(js-parser): keep plain comments within two lines

Condense the fourteen comments the diff grows past the two-line limit, keeping the invariant each one records.