feat(compress): split MT stream drain policy

The MT stream initializer previously exposed one C callback that waited for
all submitted jobs and then released their resources. That left the ordering
policy in C even though Rust already owned the surrounding initialization
sequence and the ring-order wait/release policies.

Expose separate wait-all and release-all callbacks at the Rust/C boundary and
invoke them in Rust in the original wait-before-release order. C retains the
worker synchronization, job descriptors, input buffer, and resource-pool
side effects behind the two callbacks, while the focused Rust initializer test
now makes the ordering explicit.

Test Plan:
- capped cargo +nightly fmt for the Rust workspace -- passed
- capped root cargo clippy --all-targets -- -D warnings -- passed
- capped serial make -j1 for the single-threaded library, MT library, and CLI -- passed
- git diff --cached --check -- passed

lib/compress/zstdmt_compress.c

@@ -756,7 +756,8 @@ typedef struct {
     unsigned allJobsCompleted;
 } ZSTDMT_RustInitCStreamProjection;
 typedef size_t (*ZSTDMT_initResizeFn)(void* opaque, unsigned nbWorkers);
-typedef void (*ZSTDMT_initDrainFn)(void* opaque);
+typedef void (*ZSTDMT_initWaitForAllJobsFn)(void* opaque);
+typedef void (*ZSTDMT_initReleaseAllJobResourcesFn)(void* opaque);
 typedef void (*ZSTDMT_initApplyParametersFn)(void* opaque, size_t jobSize);
 typedef size_t (*ZSTDMT_initDictionaryFn)(void* opaque);
 typedef void (*ZSTDMT_initSetSizeFn)(void* opaque, size_t size);
@@ -938,7 +939,9 @@ void* ZSTDMT_rust_createCCtx(
         ZSTDMT_createCCtxFreeFn freeContext);
 size_t ZSTDMT_rust_initCStream(
         const ZSTDMT_RustInitCStreamProjection* projection, void* opaque,
-        ZSTDMT_initResizeFn resize, ZSTDMT_initDrainFn drain,
+        ZSTDMT_initResizeFn resize,
+        ZSTDMT_initWaitForAllJobsFn waitForAllJobs,
+        ZSTDMT_initReleaseAllJobResourcesFn releaseAllJobResources,
         ZSTDMT_initApplyParametersFn applyParameters,
         ZSTDMT_initDictionaryFn prepareDictionary,
         ZSTDMT_initSetSizeFn setTargetPrefixSize,
@@ -2782,13 +2785,16 @@ static size_t ZSTDMT_initCStreamResize(void* opaque, unsigned nbWorkers)
     return ZSTDMT_resize(state->mtctx, nbWorkers);
 }
 
-static void ZSTDMT_initCStreamDrain(void* opaque)
+static void ZSTDMT_initCStreamWaitForAllJobs(void* opaque)
 {
     ZSTDMT_initCStreamState* const state = (ZSTDMT_initCStreamState*)opaque;
-    ZSTDMT_CCtx* const mtctx = state->mtctx;
-    ZSTDMT_waitForAllJobsCompleted(mtctx);
-    ZSTDMT_releaseAllJobResources(mtctx);
-    mtctx->allJobsCompleted = 1;
+    ZSTDMT_waitForAllJobsCompleted(state->mtctx);
+}
+
+static void ZSTDMT_initCStreamReleaseAllJobResources(void* opaque)
+{
+    ZSTDMT_initCStreamState* const state = (ZSTDMT_initCStreamState*)opaque;
+    ZSTDMT_releaseAllJobResources(state->mtctx);
 }
 
 static void ZSTDMT_initCStreamApplyParameters(void* opaque, size_t jobSize)
@@ -3031,7 +3037,8 @@ size_t ZSTDMT_initCStream_internal(
     return ZSTDMT_rust_initCStream(
         &projection, &state,
         ZSTDMT_initCStreamResize,
-        ZSTDMT_initCStreamDrain,
+        ZSTDMT_initCStreamWaitForAllJobs,
+        ZSTDMT_initCStreamReleaseAllJobResources,
         ZSTDMT_initCStreamApplyParameters,
         ZSTDMT_initCStreamPrepareDictionary,
         ZSTDMT_initCStreamSetTargetPrefixSize,