refactor(compress): expose LDM skip leaves from Rust

Keep the existing internal ZSTD_ldm_* ABI names while making the two
sequence-store skip operations direct Rust exports. Remove only the C
forwarding declarations and bodies; LDM state projection, configuration
constants, and block-compressor adapters remain in C.

Test Plan:
- clang -fsyntax-only on lib/compress/zstd_ldm.c
- git diff --check
- Full capped native/upstream suite pending after this commit

lib/compress/zstd_ldm.c

@@ -265,8 +265,6 @@ size_t ZSTD_rust_ldm_generateSequences(
         void* hashTable, BYTE* bucketOffsets, void* window, U32* loadedDictEnd,
         void* rawSeqStore, const void* params,
         const void* src, size_t srcSize, int overflowCorrectFrequently);
-void ZSTD_rust_ldm_skipSequences(void* rawSeqStore, size_t srcSize, U32 minMatch);
-void ZSTD_rust_ldm_skipRawSeqStoreBytes(void* rawSeqStore, size_t nbBytes);
 size_t ZSTD_rust_ldm_blockCompress(
         void* rawSeqStore, void* blockContext, void* seqStore, U32 rep[ZSTD_REP_NUM],
         const void* src, size_t srcSize, U32 minMatch, int strategy);
@@ -387,17 +385,6 @@ size_t ZSTD_ldm_generateSequences(
             ZSTD_WINDOW_OVERFLOW_CORRECT_FREQUENTLY);
 }
 
-void ZSTD_ldm_skipSequences(RawSeqStore_t* rawSeqStore, size_t srcSize,
-                            U32 const minMatch)
-{
-    ZSTD_rust_ldm_skipSequences(rawSeqStore, srcSize, minMatch);
-}
-
-void ZSTD_ldm_skipRawSeqStoreBytes(RawSeqStore_t* rawSeqStore, size_t nbBytes)
-{
-    ZSTD_rust_ldm_skipRawSeqStoreBytes(rawSeqStore, nbBytes);
-}
-
 size_t ZSTD_ldm_blockCompress(RawSeqStore_t* rawSeqStore,
     ZSTD_MatchState_t* ms, SeqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
     ZSTD_ParamSwitch_e useRowMatchFinder,