[Feature] Add efficient batched runtime block mutations for simulation-style mods

[yunnwi]

Problem / Motivation

Simulation-style mods currently need to emit many individual SetBlock mutations from lifecycle callbacks.

This is awkward and fragile for mods such as:

• cellular automata
• spreading/infection blocks
• machines
• redstone-like systems
• falling-sand style simulations

In testing a 64x64 Conway Life-style Wasm mod, large repeated SetBlock batches caused tick instability unless mutation output was heavily capped.

Proposed solution

Add an efficient batched runtime block mutation api.

Possible shapes:

• SetBlocks(Vec<(pos, block_id)>)
• runtime FillBox, not only worldgen FillBox
• chunk-local mutation batches
• explicit accepted/rejected mutation counts
• clear diagnostics when callback result size or mutation budget is exceeded

Alternatives considered

Current workaround:

• cap mutations per tick
• run simulation less frequently
• keep state inside the mod and only emit a small number of visual updates

This works, but makes simulation mods less responsive and harder to reason about.