feat(compress): move block-state confirmation to Rust

Keep C ownership of the block-state structure while delegating the confirmed-block pointer swap through a narrow two-pointer ABI leaf. Preserve every existing confirmation call site and add direct pointer-swap coverage.

Test Plan:

- cargo test --manifest-path rust/Cargo.toml --no-default-features --features compression

- cargo clippy --manifest-path rust/Cargo.toml --no-default-features --features compression --all-targets

- cargo +nightly fmt --manifest-path rust/Cargo.toml

- make -B -C lib -j2 lib

- tests/fuzzer -s4560 -t47 -i48 -v

- make -C tests -j2 test-zstream

lib/compress/zstd_compress.c

@@ -269,6 +269,9 @@ size_t ZSTD_rust_copyBlockSequences(
         SeqCollector* seqCollector, const SeqStore_t* seqStore,
         const U32 prevRepcodes[ZSTD_REP_NUM]);
 void ZSTD_rust_resetCompressedBlockState(ZSTD_compressedBlockState_t* bs);
+void ZSTD_rust_confirmRepcodesAndEntropyTables(
+        ZSTD_compressedBlockState_t** prevCBlock,
+        ZSTD_compressedBlockState_t** nextCBlock);
 void ZSTD_rust_storeLastLiterals(SeqStore_t* seqStorePtr,
                                  const BYTE* anchor, size_t lastLLSize);
 void ZSTD_rust_resetSeqStore(SeqStore_t* ssPtr);
@@ -2596,9 +2599,8 @@ static int ZSTD_maybeRLE(SeqStore_t const* seqStore)
 static void
 ZSTD_blockState_confirmRepcodesAndEntropyTables(ZSTD_blockState_t* const bs)
 {
-    ZSTD_compressedBlockState_t* const tmp = bs->prevCBlock;
-    bs->prevCBlock = bs->nextCBlock;
-    bs->nextCBlock = tmp;
+    ZSTD_rust_confirmRepcodesAndEntropyTables(
+            &bs->prevCBlock, &bs->nextCBlock);
 }
 
 /* Writes the block header */