Implement SetSyscall (syscall 0x74) with safe override/fallback dispatch

[Whoneon]

This PR implements numeric syscall 0x74 as SetSyscall, with runtime override support for numeric syscalls. This was discussed before in #93

Motivation

Generated code from Burnout 3 (SLUS 210.50) shows explicit syscall usage with $v1 = 0x74 (SetSyscall). This has been confirmed by looking at PS2Tek and ps2sdk syscallnr.h and using them as SoT

What changed

• 0x74 now dispatches to SetSyscall.
• Added a thread-safe override table: syscallIndex -> handlerAddress.
• Added pre-dispatch override resolution:
  • if override exists and can be invoked, use it
  • if invocation fails/missing target, fall back to built-in numeric syscall handling
• Cleared override table in runtime teardown.
• Added SetSyscall to the call-list X-macro.

Tests

Added kernel runtime tests that verify:

1. override install + execution + returned v0
2. override clear and return to built-in behavior
3. fallback to built-in when override target is not registered

[ran-j]

Please don't remove exit. Move it to correct syscall id

[ran-j]

Can you explain what is this function?

[Whoneon]

It checks whether a given numeric syscall has a runtime override registered. If found and is callable, the function forwards execution there and returns true. If no valid override exists, it returns false

[ran-j]

I was playing around with this and I think I found a bug. I will confirm later.