feat: Add per-class identityMode via @JS macro parameter

[krodak]

Overview

Add identityMode: Bool parameter to the @JS macro, enabling per-class opt-in to pointer identity caching. Identity is resolved entirely at codegen time - no runtime option.

@JS(identityMode: true)
class BuildingBridged { ... }  // identity caching enabled

@JS
class TemporaryObject { ... }  // no caching (default)

@JS(identityMode: false)
class ExplicitlyUncached { ... }  // explicitly opted out, even if config says pointer

Resolution: @JS(identityMode: true/false) > bridge-js.config.json > default (off).

The runtime options.identityMode override has been removed. Benchmarking both modes requires separate builds. This keeps the generated code simple: each class's __construct either passes __identityCache or null to __wrap, no runtime branching.

Links

• ClickUp initiative: BridgeJS Pointer Identity Mode
• Builds on PR feat: Add opt-in identityMode pointer for SwiftHeapObject wrapper identity caching #2 (merged)

What changed

• Macros.swift - Added identityMode: Bool = false parameter to @JS macro.
• BridgeJSSkeleton.swift - Added identityMode: Bool? to ExportedClass.
• SwiftToSkeleton.swift - Added extractIdentityMode parser, same pattern as extractNamespace/extractEnumStyle.
• BridgeJSLink.swift - Per-class codegen: classes with identity get __identityCache passed to __wrap, others get null. Removed global shouldUseIdentityMap, identityMode runtime variable, and hasIdentitySupport check. Added shouldUseIdentityCache(for:) helper.
• instantiate.d.ts / index.js / index.d.ts - Removed identityMode from InstantiateOptions and Options types. Removed runtime pass-through in node/browser init.
• IdentityModeClass.swift - Test input with @JS(identityMode: true), plain @JS, and @JS(identityMode: false).
• BridgeJSLinkTests.swift - Tests: per-class annotation parsing, config "pointer" + class override, skeleton-level assertions.
• All snapshot files - Updated with simplified per-class codegen.

Tested

• swift test --package-path ./Plugins/BridgeJS - 107 tests pass
• ./Utilities/format.swift - clean
• ./Utilities/bridge-js-generate.sh - generated files up to date

[krodak]

Benchmark Results (PR #3 vs PR #2)

Release build, adaptive sampling with IQR outlier removal. arm64-apple-macosx26.0, Node.js v22.22.0.

Moving identity mode from runtime flag to codegen-time decision improved performance across the board. V8 JIT optimizes better when __construct passes the cache directly (no runtime conditional) and __wrap checks a parameter instead of a global variable.

Scenario	No identity	PR #2 pointer	PR #3 pointer	vs baseline
passBothWaysRoundtrip (1M)	245 ms	64 ms	48 ms	5.1x faster
swiftConsumesSameObject (1M)	21 ms	30 ms	11 ms	1.9x faster
churnObjects (100k)	133 ms	117 ms	111 ms	1.2x faster
swiftCreatesObject (1M)	696 ms	2147 ms	2216 ms	3.2x slower

swiftConsumesSameObject flipped from 1.4x slower (PR #2) to 1.9x faster (PR #3) because the non-identity __wrap path no longer checks a global flag.

Memory unchanged: 271 MiB → 41 MiB peak heap (6.6x), 271 MiB → 21 MiB retained (12.9x).