feat(compress): move reduce-index policy into Rust

Move match-table selection and btlazy2 marker policy out of the C overflow
correction wrapper. Rust now decides whether chain and hash3 tables
participate using the strategy, row-matchfinder, dedicated-dictionary, and
log inputs, then delegates cell updates to the existing Rust reducer. C
retains only the private table pointers and scalar projection.

Test Plan:
- cargo fmt --manifest-path rust/Cargo.toml -- --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 test --manifest-path rust/Cargo.toml zstd_compress::tests::reduce_index_for_match_state -- --nocapture
- ulimit -v 41943040 && make -j1
- ulimit -v 41943040 && make -j1 -C tests test-fuzzer FUZZERTEST=-T3s FUZZER_FLAGS=--no-big-tests

lib/compress/zstd_compress.c

@@ -656,6 +656,12 @@ void ZSTD_rust_reduceIndex(U32* hashTable, U32 hashSize,
                            U32* chainTable, U32 chainSize,
                            U32* hashTable3, U32 hashSize3,
                            U32 reducerValue, int preserveChainMark);
+void ZSTD_rust_reduceIndexForMatchState(
+        U32* hashTable, U32 hashLog,
+        U32* chainTable, U32 chainLog,
+        U32* hashTable3, U32 hashLog3,
+        int strategy, int useRowMatchFinder, int dedicatedDictSearch,
+        U32 reducerValue);
 typedef int (*ZSTD_rust_overflowNeedCorrection_f)(
         void* context, const void* src, const void* srcEnd);
 typedef U32 (*ZSTD_rust_overflowCorrect_f)(
@@ -4803,27 +4809,12 @@ size_t ZSTD_copyCCtx(ZSTD_CCtx* dstCCtx, const ZSTD_CCtx* srcCCtx, unsigned long
 *   rescale all indexes to avoid future overflow (indexes are U32) */
 static void ZSTD_reduceIndex (ZSTD_MatchState_t* ms, ZSTD_CCtx_params const* params, const U32 reducerValue)
 {
-    U32 const hSize = (U32)1 << params->cParams.hashLog;
-    U32* chainTable = NULL;
-    U32 chainSize = 0;
-    U32* hashTable3 = NULL;
-    U32 hashSize3 = 0;
-
-    if (ZSTD_allocateChainTable(params->cParams.strategy, params->useRowMatchFinder, (U32)ms->dedicatedDictSearch)) {
-        chainTable = ms->chainTable;
-        chainSize = (U32)1 << params->cParams.chainLog;
-    }
-
-    if (ms->hashLog3) {
-        hashTable3 = ms->hashTable3;
-        hashSize3 = (U32)1 << ms->hashLog3;
-    }
-
-    ZSTD_rust_reduceIndex(ms->hashTable, hSize,
-                          chainTable, chainSize,
-                          hashTable3, hashSize3,
-                          reducerValue,
-                          params->cParams.strategy == ZSTD_btlazy2);
+    ZSTD_rust_reduceIndexForMatchState(
+            ms->hashTable, params->cParams.hashLog,
+            ms->chainTable, params->cParams.chainLog,
+            ms->hashTable3, ms->hashLog3,
+            params->cParams.strategy, params->useRowMatchFinder,
+            ms->dedicatedDictSearch, reducerValue);
 }