Expose managed NPC awareness events

[diffuin]

Summary

• Exposes the eight native NPC awareness callbacks as managed S1API events.
• Adds the read-only NPCNoiseEvent snapshot and managed NPCNoiseType enum.
• Subscribes each mod handler directly to its native UnityEvent while converting player, vehicle, and noise arguments at the API boundary.
• Stores the exact native UnityAction<T> and UnityEvent for independent removal and cleanup on both runtimes.
• Keeps registration state lazy for joined-client wrappers created without constructors.

Dependency

This branch is stacked on #267 to resolve their shared NPC event and cleanup surface. Merge #267 first; this PR then reduces to the awareness API changes.

Validation

• MonoMelon full suite: 592 passed.
• Il2CppMelon full suite: 581 passed.
• Mono gameplay smoke: all vehicle and awareness scenarios passed in Main against head e6187d4.
• IL2CPP gameplay smoke: all vehicle and awareness scenarios passed in Main against head e6187d4.
• Runtime probe covered all five player-awareness events, gunshot and explosion snapshots, hit-by-car conversion, native vehicle entry/exit, duplicate registration, one-at-a-time removal, final unsubscription, and throwing-subscriber isolation.
• Runtime-neutral contract tests avoid loading Unity runtime internals in the Linux CI host.
• git diff --check passed.

Closes #244