refactor(compress): move MT parameter update policy to Rust

Move the next-job parameter derivation in
ZSTDMT_updateCParams_whileCompressing() behind a scalar Rust projection. Rust
now reproduces the existing CCtx-parameter derivation and restores the active
frame's saved windowLog; C retains private MT/CCtx layouts, logging, and final
writes.

Expose the preprocessor-derived block-compressor exclusion mask through the
private C boundary so reduced builds keep their authoritative configuration.
Add C/Rust layout assertions and focused tests for window preservation and
strategy-exclusion routing.

Test Plan:
- `ulimit -v 41943040; cargo +nightly fmt --manifest-path rust/Cargo.toml --all -- --check`
- `ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo clippy --manifest-path rust/Cargo.toml --all-targets -- -D warnings`
- `ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo clippy --manifest-path rust/cli/Cargo.toml --all-targets -- -D warnings`
- `ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo test --manifest-path rust/cli/Cargo.toml --all-targets` (184 tests)
- `ulimit -v 41943040; make -j1`
- `ulimit -v 41943040; make -j1 -C tests test` (all upstream tests completed successfully)
- Standalone Rust unit linking remains unavailable without the C-owned bridge symbols; integrated build and upstream MT/API coverage passed.

lib/compress/zstd_compress.c

@@ -3945,7 +3945,7 @@ U32 ZSTD_cycleLog(U32 hashLog, ZSTD_strategy strat)
     return ZSTD_rust_params_cycleLog(hashLog, (int)strat);
 }
 
-static U32 ZSTD_getCParamsExclusionMask(void);
+U32 ZSTD_getCParamsExclusionMask(void);
 
 /** ZSTD_adjustCParams_internal() :
  *  optimize `cPar` for a specified input (`srcSize` and `dictSize`).
@@ -4001,7 +4001,7 @@ enum {
     ZSTD_RUST_PARAMS_EXCLUDE_DFAST = 1u << 6
 };
 
-static U32 ZSTD_getCParamsExclusionMask(void)
+U32 ZSTD_getCParamsExclusionMask(void)
 {
     U32 mask = 0;
 #ifdef ZSTD_EXCLUDE_BTULTRA_BLOCK_COMPRESSOR