refactor(compress): move stable buffer policy to Rust

Move the stable input and output expectation update into the Rust compression
module. Keep the private CCtx layout and debug logging in the C adapter while
passing only the buffer-mode scalars and projected buffer fields across the
ABI. Preserve C size_t wrapping for the output remainder and leave buffered
modes unchanged.

Test Plan:
- rustfmt --edition 2021 --check rust/src/zstd_compress.rs
- ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo clippy --manifest-path rust/Cargo.toml --all-targets -- -D warnings
- ulimit -v 41943040; make -j1
- ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo test --manifest-path rust/Cargo.toml --all-targets
- ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo test --manifest-path rust/cli/Cargo.toml --all-targets
- ulimit -v 41943040; make -j1 -C tests test

lib/compress/zstd_compress.c

@@ -1792,6 +1792,10 @@ size_t ZSTD_rust_checkBufferStability(
         const void* expectedInSrc, size_t expectedInPos,
         const void* inputSrc, size_t inputPos,
         size_t expectedOutBufferSize, size_t outputSize, size_t outputPos);
+void ZSTD_rust_setBufferExpectations(
+        int inBufferMode, int outBufferMode,
+        ZSTD_inBuffer* expectedInBuffer, size_t* expectedOutBufferSize,
+        const ZSTD_outBuffer* output, const ZSTD_inBuffer* input);
 
 /* Context-free compression-parameter selection and sizing leaves live in
  * Rust (rust/src/zstd_compress_params.rs).  This file retains
@@ -7690,12 +7694,13 @@ static void
 ZSTD_setBufferExpectations(ZSTD_CCtx* cctx, const ZSTD_outBuffer* output, const ZSTD_inBuffer* input)
 {
     DEBUGLOG(5, "ZSTD_setBufferExpectations (for advanced stable in/out modes)");
-    if (cctx->appliedParams.inBufferMode == ZSTD_bm_stable) {
-        cctx->expectedInBuffer = *input;
-    }
-    if (cctx->appliedParams.outBufferMode == ZSTD_bm_stable) {
-        cctx->expectedOutBufferSize = output->size - output->pos;
-    }
+    ZSTD_rust_setBufferExpectations(
+            (int)cctx->appliedParams.inBufferMode,
+            (int)cctx->appliedParams.outBufferMode,
+            &cctx->expectedInBuffer,
+            &cctx->expectedOutBufferSize,
+            output,
+            input);
 }
 
 /* Validate that the input/output buffers match the expectations set by