Pair AiArrayMapConst with AiArrayUnmapConst in prim writer

[kikou]

Summary

• In UsdArnoldPrimWriter::_WriteArnoldParameters, the per-type branches read array data via AiArrayMapConst(array) but seven branches unmapped it with the non-const AiArrayUnmap(array): AI_TYPE_BYTE, AI_TYPE_BOOLEAN, AI_TYPE_RGB, AI_TYPE_VECTOR, AI_TYPE_RGBA, AI_TYPE_VECTOR2, AI_TYPE_MATRIX.
• The remaining branches (AI_TYPE_INT, AI_TYPE_UINT, AI_TYPE_FLOAT) already used the matching AiArrayUnmapConst.
• Mismatching the const / non-const pair flags the array as modified even though it was only read, which can trigger spurious copies or write-backs on shared array data.
• Switched the seven mismatched sites to AiArrayUnmapConst. The only remaining non-const AiArrayMap/AiArrayUnmap pair in the file (the shidxs write site) is unchanged.

Test plan

• Export a scene that exercises the affected attribute types (byte/bool/rgb/vec/rgba/vec2/matrix arrays — e.g. instance visibility, color/normal/uv arrays, instance matrices) via the USD writer and confirm the written values match what's written today.
• No new warnings/asserts from the Arnold core around array map/unmap.