Add biome uniform-section fast-path

[ByteExceptionM]

Most biome sections in a world are uniform (same biome across all 64 cells). Instead of always computing a full 4096-entry BitArray, we now check if all entries are the same first and use a SingletonBitArray in that case. Skips a lot of unnecessary work for the common case.

[Copilot]

Pull request overview

This PR optimizes biome section serialization by detecting uniform biome sections (all 64 biome cells use the same palette index) and emitting a singleton-backed BlockStorage instead of expanding into a full 4096-entry BitArray, reducing work for the common case.

Changes:

• Add a uniform-section detection loop over the 64 biome cells in a section.
• When uniform, construct BlockStorage using SingletonBitArray with a single-entry Bedrock biome palette.
• Preserve existing behavior for non-uniform sections by building the full BitArray and translated palette.

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[valaphee]

allSame should never occur, as this would indicate a SingletonPalette.

[ByteExceptionM]

allSame should never occur, as this would indicate a SingletonPalette.

Tested this on a proxy - added a debug log on the fast-path. Under normal player load it hits hundreds of times per second.

Logs:

Code used for the test:

So there are real cases where a non-Singleton palette is sent but all 64 cells point to the same index. I didn't look into the exact server-side reason, but it happens a lot in practice and the fast-path skips the full 4096-entry BitArray expansion for it.

[valaphee]

Which server software are you using and whats the content of the palette? If the palette contains an entry multiple times or unreferenced ones then it should be considered a bug by the server implementation.

[valaphee]

code-wise LGTM

[onebeastchris]

Thanks!