feat(rust): add common primitive compatibility layer

Introduce the Rust static library and move the shared byte, bitstream, CPU,
error, xxHash, debug, and public-common implementations into it. Thin C shims
preserve the existing header-driven C build while original tests link the Rust
archive.

This establishes the ABI-safe foundation for later codec and CLI ports;
entropy coding, runtime support, codecs, dictionaries, and the CLI remain C.
The top-down migration map documents that boundary and its validation path.

Test Plan:
- cargo fmt --check
- cargo test --all-targets
- cargo clippy --all-targets -- -D warnings
- cargo build --release

Refs: rust/README.md

lib/common/zstd_common.c

@@ -1,48 +1,10 @@
-/*
- * Copyright (c) Meta Platforms, Inc. and affiliates.
- * All rights reserved.
- *
- * This source code is licensed under both the BSD-style license (found in the
- * LICENSE file in the root directory of this source tree) and the GPLv2 (found
- * in the COPYING file in the root directory of this source tree).
- * You may select, at your option, one of the above-listed licenses.
- */
-
-
-
-/*-*************************************
-*  Dependencies
-***************************************/
-#define ZSTD_DEPS_NEED_MALLOC
 #include "error_private.h"
 #include "zstd_internal.h"
 
-
-/*-****************************************
-*  Version
-******************************************/
-unsigned ZSTD_versionNumber(void) { return ZSTD_VERSION_NUMBER; }
-
-const char* ZSTD_versionString(void) { return ZSTD_VERSION_STRING; }
-
-
-/*-****************************************
-*  ZSTD Error Management
-******************************************/
-#undef ZSTD_isError   /* defined within zstd_internal.h */
-/*! ZSTD_isError() :
- *  tells if a return value is an error code
- *  symbol is required for external callers */
-unsigned ZSTD_isError(size_t code) { return ERR_isError(code); }
-
-/*! ZSTD_getErrorName() :
- *  provides error code string from function result (useful for debugging) */
-const char* ZSTD_getErrorName(size_t code) { return ERR_getErrorName(code); }
-
-/*! ZSTD_getError() :
- *  convert a `size_t` function result into a proper ZSTD_errorCode enum */
-ZSTD_ErrorCode ZSTD_getErrorCode(size_t code) { return ERR_getErrorCode(code); }
-
-/*! ZSTD_getErrorString() :
- *  provides error code string from enum */
-const char* ZSTD_getErrorString(ZSTD_ErrorCode code) { return ERR_getErrorString(code); }
+/* Implementation moved to Rust (rust/src/zstd_common.rs) */
+extern unsigned ZSTD_versionNumber(void);
+extern const char* ZSTD_versionString(void);
+extern unsigned ZSTD_isError(size_t code);
+extern const char* ZSTD_getErrorName(size_t code);
+extern ZSTD_ErrorCode ZSTD_getErrorCode(size_t code);
+extern const char* ZSTD_getErrorString(ZSTD_ErrorCode code);