Bound loaded Objective-C RW extension arrays - #91

Purpose

Closes #87 by advancing the Objective-C metadata reader cohort so loaded class_rw_ext_t method, property, and protocol list arrays no longer dereference unchecked runtime metadata.

Changes

• Pin MachOObjCSection cc9a70f and the matching MachOSwiftSection cohort 905703af.
• Decode single, pointer-array, and relative RW-extension representations through bounded snapshot reads, checked arithmetic, shared count and byte budgets, and per-entry diagnostics.
• Preserve existing compatibility projections while exposing typed representation and partial-result diagnostics from one owner.
• Render the new RW-extension owner and unavailable-relative-image failure in PrivateHeaderKit diagnostics.
• Document that the dependency surface is bounded while the current PrivateHeaderKit raw dump continues to query class RO member lists.

Testing

• MachOObjCSection focused iOS and watchOS 27 drop canonicalized Objective-C protocol conformances #60/Resolve all loaded entries in Objective-C relative method and property lists #65/Objective-C metadata reads can still terminate iOS 27 helpers with FileIO.offsetOutOfBounds #79/Unchecked Objective-C table and loaded-image reads can still trap on malformed metadata #83/Loaded Objective-C RW extension arrays bypass bounded list readers #87/File-backed Objective-C root sections bypass checked coordinates and table reads #88 union: 123 tests passed.
• MachOObjCSection deterministic package suite: passed, including 15 new RW-extension tests. The pre-existing host-only MachOObjCSectionTests fixture failure caused by missing /Users/JH/Downloads/iOS18.5-SwiftUI was reproduced unchanged at base 8f0ff76 and excluded from this deterministic run.
• MachOObjCSection Release builds: macOS, iOS 13 arm64, watchOS 6 arm64, and watchOS 6 arm64_32.
• Exact iOS 27 24A5390f arm64 Simulator probe: zero plus tags 0/1/2 for method, property, and protocol fields; array offset/stride 8; relative header/table offset and stride 8; unloaded-entry omission; class_copy*List count parity. The disposable device was deleted and runtime matching was restored byte-for-byte.
• MachOSwiftSection Debug and Release product builds plus 6 ObjC ancestor tests.
• PrivateHeaderKit swift test and scripts/test-release-scripts.sh.
• PrivateHeaderKit macOS Release build, iOS Core/CoreTests compile, and watchOS Core/CoreTests/helper compile. The final watch helper reports WATCHOSSIMULATOR in LC_BUILD_VERSION.
• Branch-wide codex-review: no findings for MachOObjCSection, MachOSwiftSection, or PrivateHeaderKit.

Notes

• Simulator arm64 does not verify arm64e pointer authentication; that remains an explicit unverified condition.
• No screenshots are applicable.