Fix Unity 6 native class resolver hooks

[FrozenAlex]

beatsaber-hook 9.3.0 separates its callable compatibility APIs from Unity's native class entry points. Custom-types still hooks the compatibility pointer addresses, so Unity's internal calls can bypass custom-type handling and fail during class initialization.

Update the Unity 6 hooks to target the native entry points with their actual signatures:

• Hook Class_FromIl2CppTypeNative as Il2CppClass*(const Il2CppType*, bool), preserving throwOnError when forwarding ordinary types.
• Hook Class_InitNative as void(Il2CppClass*), retaining the existing skip for registered custom classes.
• Require beatsaber-hook ^9.3.0 and update the resolved dependency and artifact URLs. Earlier Unity branches retain their existing hook signatures.

Companion to beatsaber-hook #67, released in 9.3.0. Consumers can continue using the existing callable APIs.

Validation:

• Clean NDK 29 ARM64 build and QMOD packaging against the published hook 9.3.0 package, without a local dependency override. The restored hook binary matches the published SHA-256 digest.
• This exact src/register.cpp implementation was previously tested on Quest 3 / Beat Saber 1.45.3 / Unity 6000.3.19f1 with the companion hook changes: two fresh processes each passed 752 resolver checks and 3,048 checks across 277 registered custom classes, followed by 30 seconds without a fatal log entry.
• User-confirmed in-game reloads, noticeboard scrolling, and custom-map entry/return passed. Logs recorded both reloads and two map-to-menu round trips in the same production process.

The headset tests used the previously built local hook/custom-types pair; this PR's fresh build against the published 9.3.0 artifact has not been separately deployed. Uncached generic error paths and the complete registered test suite were not exercised. An initial diagnostic-time crash during live observer patching was excluded; the corrected harness produced the clean repeat results above.