Clarify SimdSetAmxFull API semantics in SimdLib.h

[Copilot]

SimdSetAmxFull was documented too loosely relative to its actual behavior. This updates the API comment in SimdLib.h to describe the real AMX-specific effect and its runtime applicability.

• Scope of the API

  • Reworded the summary to state that the function loads the full AMX tile configuration for the current thread.

• Behavioral semantics

  • Documented that the function applies on x86 with AMX-BF16 support.
  • Clarified that it forces loading the library’s predefined full AMX tile layout via the AMX tile configuration path.

• Runtime applicability

  • Clarified that the function is a no-op when AMX-BF16 is unavailable or the corresponding SIMD backend is not enabled at runtime.

// Loads the library's full AMX tile configuration for the current thread
SimdSetAmxFull();