feat(compress): move advanced CDict sizing arithmetic into Rust

Move the advanced-CDict workspace-size formula and its by-reference,
by-copy, row-match-finder, and dedicated-search branches into the Rust
compression-parameter layer. Keep private C layout constants and the
already-resolved mode at the C boundary, where the allocator still owns
private object layout details.

Add a focused test covering the load-method and dedicated-search deltas
and the exported advanced-sizing boundary.

Test Plan:
- ulimit -v 41943040 && CARGO_BUILD_JOBS=1 cargo test --manifest-path rust/Cargo.toml
- 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 && make -j1 -C tests test-zstream ZSTREAM_TESTTIME=-T2s
- ulimit -v 41943040 && make -j1 -C tests test-fuzzer FUZZERTEST=-T3s FUZZER_FLAGS=--no-big-tests
- ulimit -v 41943040 && cargo fmt --manifest-path rust/Cargo.toml -- --check
- git diff --check

lib/compress/zstd_compress.c

@@ -1818,6 +1818,10 @@ typedef struct {
 size_t ZSTD_rust_params_estimateCDictSizeFromCParams(
         size_t dictSize, ZSTD_compressionParameters cParams,
         int dictLoadMethod, const ZSTD_rustCDictSizing* sizing);
+size_t ZSTD_rust_params_estimateCDictWorkspaceSize(
+        size_t dictSize, ZSTD_compressionParameters cParams,
+        int dictLoadMethod, int useRowMatchFinder,
+        int enableDedicatedDictSearch, const ZSTD_rustCDictSizing* sizing);
 
 /* Sequence statistics and seqStore entropy compression live in Rust
  * (rust/src/zstd_compress_stats.rs), which also exports ZSTD_seqToCodes()
@@ -6681,14 +6685,19 @@ static size_t ZSTD_rust_createCDictAdvanced_workspaceSize(
 {
     (void)context;
     if (cParams == NULL) return 0;
-    return ZSTD_cwksp_alloc_size(sizeof(ZSTD_CDict))
-         + ZSTD_cwksp_alloc_size(HUF_WORKSPACE_SIZE)
-         + ZSTD_sizeof_matchState(cParams,
-                                  (ZSTD_ParamSwitch_e)useRowMatchFinder,
-                                  enableDedicatedDictSearch,
-                                  /* forCCtx */ 0)
-         + (dictLoadMethod == ZSTD_dlm_byRef ? 0
-            : ZSTD_cwksp_alloc_size(ZSTD_cwksp_align(dictSize, sizeof(void*))));
+    {   ZSTD_rustCDictSizing const sizing = {
+            sizeof(ZSTD_CDict),
+            HUF_WORKSPACE_SIZE,
+            ZSTD_HASHLOG3_MAX,
+            sizeof(ZSTD_match_t),
+            sizeof(ZSTD_optimal_t),
+            ZSTD_RUST_ASAN_REDZONE_SIZE
+        };
+        return ZSTD_rust_params_estimateCDictWorkspaceSize(
+                dictSize, *cParams, dictLoadMethod,
+                useRowMatchFinder, enableDedicatedDictSearch,
+                &sizing);
+    }
 }
 
 static void* ZSTD_rust_createCDictAdvanced_allocate(