feat(mt): move serial failure turn policy into Rust

Move the scalar failed-job skip decision and wrapping next-job transition into
Rust. C keeps the serial mutex, error assertion, condition broadcast, and LDM
window cleanup around the projected result.

Test Plan:
- ulimit -v 41943040; CARGO_BUILD_JOBS=1; cargo test --manifest-path rust/Cargo.toml
- ulimit -v 41943040; CARGO_BUILD_JOBS=1; cargo clippy --manifest-path rust/Cargo.toml --all-targets -- -D warnings
- ulimit -v 41943040; make -B -C programs -j1 zstd
- ulimit -v 41943040; make -C tests -j1 test-zstream ZSTREAM_TESTTIME=-T1s

lib/compress/zstdmt_compress.c

@@ -368,6 +368,12 @@ void ZSTDMT_rust_serialStateGenSequences(
         ZSTDMT_serialGenerateLdmFn generateLdm,
         ZSTDMT_serialUpdateChecksumFn updateChecksum,
         ZSTDMT_serialAdvanceFn advance);
+typedef struct {
+    unsigned skip;
+    unsigned nextJobID;
+} ZSTDMT_RustSerialEnsureFinishedResult;
+ZSTDMT_RustSerialEnsureFinishedResult ZSTDMT_rust_serialStateEnsureFinished(
+        unsigned nextJobID, unsigned jobID);
 typedef void (*ZSTDMT_waitForLdmLockFn)(void* opaque);
 typedef int (*ZSTDMT_waitForLdmOverlapFn)(
         void* opaque, void* bufferStart, size_t bufferCapacity);
@@ -975,11 +981,14 @@ ZSTDMT_serialState_applySequences(const SerialState* serialState, /* just for an
 static void ZSTDMT_serialState_ensureFinished(SerialState* serialState,
                                               unsigned jobID, size_t cSize)
 {
+    ZSTDMT_RustSerialEnsureFinishedResult result;
     ZSTD_PTHREAD_MUTEX_LOCK(&serialState->mutex);
-    if (serialState->nextJobID <= jobID) {
+    result = ZSTDMT_rust_serialStateEnsureFinished(
+            serialState->nextJobID, jobID);
+    if (result.skip) {
         assert(ZSTD_isError(cSize)); (void)cSize;
         DEBUGLOG(5, "Skipping past job %u because of error", jobID);
-        serialState->nextJobID = jobID + 1;
+        serialState->nextJobID = result.nextJobID;
         ZSTD_pthread_cond_broadcast(&serialState->cond);
 
         ZSTD_PTHREAD_MUTEX_LOCK(&serialState->ldmWindowMutex);