Improve deinterleave API documentation

[ermig1979]

Summary

• Clarify SimdDeinterleaveUv, SimdDeinterleaveBgr, and SimdDeinterleaveBgra documentation to reflect per-channel extraction and nullable output planes.
• Clarify detection loader, info, init, prepare, and detect function documentation to reflect supported cascade formats, context lifetime, integral image requirements, scan modes, and output semantics.
• Clarify drawing and fill function documentation to reflect clipping, frame boundaries, pixel layout, row padding, and zero-fill behavior.
• Clarify bfloat16/float16 conversion and font API documentation to reflect bit-format conversion, font context lifecycle, resize behavior, measurement, and clipped alpha drawing.
• Clarify 16-bit float distance/norm and float32/uint8 conversion documentation to reflect accumulation precision, layouts, output ordering, bounds, scaling, and saturation behavior.

Testing

• git diff --check HEAD~1..HEAD
• git status --short --branch
• Not run: build or test suite, per request for the documentation tasks.

  

[Copilot]

Pull request overview

This PR refines public C API documentation in SimdLib.h, primarily clarifying behavior and usage constraints for deinterleave, object-detection, drawing/filling, font, and numeric conversion helpers.

Changes:

• Document nullable output planes and per-channel extraction semantics for UV/BGR/BGRA deinterleave APIs.
• Expand object detection cascade loader/init/prepare/detect documentation (supported cascade formats, integral image requirements, scan modes, and output semantics).
• Clarify drawing/fill/font and float conversion function documentation (clipping, padding behavior, scaling/saturation, and context lifecycle).