refactor(compress): move LDM fast-table policy to Rust

Move the strategy classification that decides whether LDM preparation fills
fast or double-fast tables into Rust.  C retains the private match-state,
configuration-specific table-fill leaves, and the existing excluded-DFAST
assertion.  Add enum-value ABI checks plus focused tests for valid and invalid
strategy classifications.

Test Plan:
- `ulimit -v 41943040; cargo +nightly fmt --manifest-path rust/Cargo.toml --all -- --check`
- `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`
- `ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo clippy --manifest-path rust/cli/Cargo.toml --all-targets -- -D warnings`
- `ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo test --manifest-path rust/cli/Cargo.toml --all-targets`

The integrated checks ran at the combined working-tree tip under a serial
40 GiB virtual-memory limit. Standalone root Rust unit linking remains
unavailable because the crate imports C-owned bridge symbols without a Cargo
build/link setup.

lib/compress/zstd_ldm.c

@@ -248,6 +248,8 @@ ZSTD_RUST_LDM_OFFSET_CHECK(
 
 #undef ZSTD_RUST_LDM_OFFSET_CHECK
 typedef char ZSTD_rust_ldm_rep_count[(ZSTD_REP_NUM == 3) ? 1 : -1];
+typedef char ZSTD_rust_ldm_strategy_values_check[
+        (ZSTD_fast == 1 && ZSTD_dfast == 2 && ZSTD_btultra2 == 9) ? 1 : -1];
 
 void ZSTD_rust_ldm_adjustParameters(
         void* params, U32 windowLog, int strategy,
@@ -270,6 +272,14 @@ size_t ZSTD_rust_ldm_blockCompress(
         const void* src, size_t srcSize, U32 minMatch, int strategy);
 U32 ZSTD_rust_ldm_limitTableUpdate(U32 curr, U32 nextToUpdate);
 
+enum {
+    ZSTD_RUST_LDM_FAST_TABLES_NONE = 0,
+    ZSTD_RUST_LDM_FAST_TABLES_FAST = 1,
+    ZSTD_RUST_LDM_FAST_TABLES_DFAST = 2
+};
+
+int ZSTD_rust_ldm_fastTableKind(int strategy);
+
 const U64* ZSTD_ldm_rust_gearTable(void);
 void ZSTD_ldm_rust_prepareBlock(void* blockContext, const void* anchor);
 size_t ZSTD_ldm_rust_compressLiterals(
@@ -289,24 +299,18 @@ typedef struct {
 
 static void ZSTD_rust_ldm_fillFastTables(ZSTD_MatchState_t* ms, const BYTE* end)
 {
-    switch (ms->cParams.strategy) {
-    case ZSTD_fast:
+    switch (ZSTD_rust_ldm_fastTableKind((int)ms->cParams.strategy)) {
+    case ZSTD_RUST_LDM_FAST_TABLES_FAST:
         ZSTD_fillHashTable(ms, end, ZSTD_dtlm_fast, ZSTD_tfp_forCCtx);
         break;
-    case ZSTD_dfast:
+    case ZSTD_RUST_LDM_FAST_TABLES_DFAST:
 #ifndef ZSTD_EXCLUDE_DFAST_BLOCK_COMPRESSOR
         ZSTD_fillDoubleHashTable(ms, end, ZSTD_dtlm_fast, ZSTD_tfp_forCCtx);
 #else
         assert(0);
 #endif
         break;
-    case ZSTD_greedy:
-    case ZSTD_lazy:
-    case ZSTD_lazy2:
-    case ZSTD_btlazy2:
-    case ZSTD_btopt:
-    case ZSTD_btultra:
-    case ZSTD_btultra2:
+    case ZSTD_RUST_LDM_FAST_TABLES_NONE:
         break;
     default:
         assert(0);