feat(compress): move pledged source setter into Rust

Move the active-stage check and pledged-size update behind a scalar Rust ABI
leaf while keeping the CCtx layout and public C entry point in C. Preserve the
stage_wrong error encoding and the unsigned wrap behavior at U64::MAX.

Test Plan:
- cargo test --manifest-path rust/Cargo.toml --lib zstd_compress::tests (80 passed)
- cargo clippy --manifest-path rust/Cargo.toml --lib -- -D warnings
- rustfmt +nightly --edition 2021 rust/src/zstd_compress.rs --check
- make -C programs -j2 zstd
- git diff --check

lib/compress/zstd_compress.c

@@ -48,6 +48,9 @@ int ZSTD_rust_updateFrameProgression(unsigned long long* consumedSrcSize,
                                      unsigned long long pledgedSrcSizePlusOne,
                                      size_t srcSize, size_t cSize,
                                      size_t fhSize);
+size_t ZSTD_rust_setPledgedSrcSize(int streamStage,
+                                   unsigned long long pledgedSrcSize,
+                                   unsigned long long* pledgedSrcSizePlusOne);
 ZSTD_frameProgression ZSTD_rust_frameProgression(U64 consumedSrcSize,
                                                   size_t buffered,
                                                   U64 producedCSize);
@@ -974,10 +977,8 @@ size_t ZSTD_CCtx_setParams(ZSTD_CCtx* cctx, ZSTD_parameters params)
 size_t ZSTD_CCtx_setPledgedSrcSize(ZSTD_CCtx* cctx, unsigned long long pledgedSrcSize)
 {
     DEBUGLOG(4, "ZSTD_CCtx_setPledgedSrcSize to %llu bytes", pledgedSrcSize);
-    RETURN_ERROR_IF(cctx->streamStage != zcss_init, stage_wrong,
-                    "Can't set pledgedSrcSize when not in init stage.");
-    cctx->pledgedSrcSizePlusOne = pledgedSrcSize+1;
-    return 0;
+    return ZSTD_rust_setPledgedSrcSize((int)cctx->streamStage, pledgedSrcSize,
+                                       &cctx->pledgedSrcSizePlusOne);
 }
 
 static ZSTD_compressionParameters ZSTD_dedicatedDictSearch_getCParams(