Export ZSTD_useTargetCBlockSize and ZSTD_blockSplitterEnabled directly from
Rust under their existing caller symbols. Remove the redundant C forwarding
wrappers while preserving diagnostics, ABI signatures, and parameter layout.
Test Plan:
- worker capped format, C syntax, and diff checks
- parent capped root clippy and native build
- parent capped upstream make -j1 -C tests test
- parent capped CLI clippy and tests
ddidderr
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