feat(compress): move window clearing leaf into Rust

Keep the private ZSTD_window_t layout and pointer-difference calculation in C,
then route the size_t-to-U32 conversion and paired limit writes through a small
Rust ABI leaf. This removes the inline C window-clear implementation while
preserving its overflow behavior at both single-threaded and multithreaded
call sites.

Test Plan:
- cargo test --manifest-path rust/Cargo.toml --lib zstd_compress::tests (77 passed)
- make -C programs -j2 zstd
- rustfmt +nightly --edition 2021 rust/src/zstd_compress.rs --check
- make -C tests -j2 test-cli-tests (41 passed)
- make -C tests -j2 test-legacy test-invalidDictionaries test-decodecorpus test-rust-lib-smoke (passed)
- git diff --check

lib/compress/zstdmt_compress.c

@@ -620,7 +620,10 @@ static void ZSTDMT_serialState_ensureFinished(SerialState* serialState,
         ZSTD_pthread_cond_broadcast(&serialState->cond);
 
         ZSTD_PTHREAD_MUTEX_LOCK(&serialState->ldmWindowMutex);
-        ZSTD_window_clear(&serialState->ldmWindow);
+        ZSTD_rust_windowClear((size_t)(serialState->ldmWindow.nextSrc -
+                                       serialState->ldmWindow.base),
+                              &serialState->ldmWindow.lowLimit,
+                              &serialState->ldmWindow.dictLimit);
         ZSTD_pthread_cond_signal(&serialState->ldmWindowCond);
         ZSTD_pthread_mutex_unlock(&serialState->ldmWindowMutex);
     }