ABI: implement exact fast built-in property reads

Parent

• #134
• #140
• #163
• #164

Scope

Implement the pinned side-effect-controlled property reads:

• JSC__JSValue__fastGetDirect_
• JSC__JSValue__fastGet
• JSC__JSValue__fastGetOwn
• Bun__JSObject__getCodePropertyVMInquiry (Bun core only)

Acceptance criteria

• Pin all 24 BuiltinName byte values, including Symbol.asyncIterator, and reject out-of-range IDs safely.
• fastGetDirect_ reads only direct own data storage and returns empty for absence/accessors without walking prototypes or invoking user code.
• fastGetOwn performs exact GetOwnProperty slot resolution, including own accessors and Proxy descriptor behavior, and returns empty for absence/exception.
• fastGet uses the existing Bun-compatible Object.prototype-cutoff lookup and returns deleted for absence, empty for exception, and present undefined unchanged.
• Bun's code VM inquiry rejects null/proxy receivers, walks data properties without invoking accessors/custom hooks, and returns empty for absence or non-pure slots.
• Focused coverage includes all 24 IDs, Symbol identity, direct/own/inherited distinctions, Object.prototype cutoff, accessors, proxies, present undefined, invalid IDs, sibling realms, foreign values, and first-exception preservation.
• Inventories, README/API evidence, and parent trackers are regenerated from checked-in results.

Implemented and published directly on main.

Implementation: 59029d2d (feat(abi): implement fast built-in property reads (#204)) Documentation: 4f9c60e6 (docs(abi): publish fast property read evidence (#204))

Delivered:

• exact 24-entry BuiltinName byte table, including VM-owned Symbol.asyncIterator and Symbol.for("nodejs.util.inspect.custom") identity;
• direct-data-only, own-slot, and Object.prototype-cutoff fast reads with their distinct empty/deleted/present-undefined contracts;
• Bun-only pure code VM inquiry that sees inherited data but executes no accessor, custom hook, or Proxy trap;
• table-wide and observability-focused coverage for accessors, proxies, inheritance, cutoff, invalid IDs, sibling realms, foreign cells, and first-exception preservation.

Validation:

• zig build test-home-private-abi -Doptimize=Debug — green, 115/115 symbols linked and runtime matrix passed.
• zig build home-private-abi-audit bun-private-abi-audit — green.
• Home: 116/431 implemented, 315 pending.
• Bun core: 110/421 implemented, 311 pending.
• Public/extension accounting remains 117/19.

README benchmark scores were preserved because this was an ABI/correctness slice and no benchmark input changed.