ABI: implement exact core structural equality

Parent: #229

Goal

Implement the shared pinned structural comparison engine plus:

• JSC__JSValue__deepEquals
• JSC__JSValue__strictDeepEquals

Acceptance

• Pairwise cycle detection with exact alias/cycle-shape matching and bounded-stack failure.
• SameValue primitive handling and ordinary enumerable string/Symbol property traversal.
• Strict versus non-strict prototype, missing/undefined, sparse-hole, and property-count distinctions.
• Exact Array, ordinary/class/null-prototype object, boxed primitive, function, Date, RegExp, Error/cause, Map, Set, ArrayBuffer, DataView, and numeric TypedArray behavior.
• Detached/shared buffers and non-strict numeric versus strict bitwise float comparison.
• Getter/proxy exceptions, same-VM siblings, foreign rejection, OOM cleanup, and first-wins pending exceptions.
• Focused matrices, fixture/inventory wiring, batched audits, README/docs evidence, small commits on origin/main.

Implemented and published on origin/main.

Evidence:

• code: 0b025285 (feat(abi): implement exact core deep equality (#230))
• documentation: 9d511f93 (docs(abi): publish core deep-equality evidence (#230))
• focused matrix: 3/3 passed, 0 skipped, 0 failed, 0 leaked
• Home fixture: 216/216 symbols linked; runtime matrix passed
• Home profile: 217/431 implemented, 214 pending
• Bun core: 211/421 implemented, 210 pending
• public audit: 117/117 public, 19 extensions, 221 private/support exports

The committed matrix covers SameValue primitives, strict/non-strict missing and hole semantics, calculated classes, boxed strings/functions, cycle correspondence and bounded recursion, Symbols, proxy/getter observability and exceptions, Map/Set, Date/RegExp/Error/cause, ArrayBuffer/DataView/numeric TypedArrays, sibling realms, foreign rejection, and first-wins pending exceptions. The benchmark artifact remains 36a617b3 because this slice changes only the private ABI boundary.