[WIP] Caching for cuslide2

[cdinea]

Description

Implements tile-level caching for cuslide2's single-region read_region() path

Key changes

• Tile-level caching (ifd.cpp)
• Decomposes each read_region() ROI into its constituent TIFF tiles, performs per-tile cache lookups via cuCIM's existing ImageCache API, decodes only cache-miss tiles via nvImageCodec, inserts decoded tiles into the cache, and assembles the final output raster.
• Reuses cuslide's cache infrastructure (create_key, find, lock/unlock, allocate, insert) — no new cache backend code.
• Fixed hash_value_ to include the file handle hash (file_hash ^ splitmix64(ifd_index)) for cross-file cache key uniqueness.
• Edge tiles are clipped to actual image bounds; decode failures fill with background_value.
• Tiles always cached in host memory; GPU output transferred via a single cudaMemcpy(H2D) after assembly.
• Falls back to direct ROI decode when caching is not applicable (strip-based images, out-of-bounds ROI, or no_cache mode).

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[cdinea]

/ok to test 87618ac

[cdinea]

/ok to test 5ee97fa