feat(rust): export public sequence helpers

Move the context-free ZSTD_sequenceBound and ZSTD_mergeBlockDelimiters APIs
into the Rust compression helper module. Preserve the public sequence ABI,
block-delimiter semantics, and unsigned literal-length wrapping behavior while
leaving context-driven sequence generation in C.

Test Plan:
- cargo clippy
- cargo clippy --benches
- cargo clippy --tests
- cargo +nightly fmt
- cargo test zstd_compress_api::tests -- --nocapture
- cargo test --target i686-unknown-linux-gnu zstd_compress_api::tests

Refs: Rust compression-bound export 3e2635f4

lib/compress/zstd_compress.c

@@ -3501,11 +3501,7 @@ static size_t ZSTD_copyBlockSequences(SeqCollector* seqCollector, const SeqStore
     return 0;
 }
 
-size_t ZSTD_sequenceBound(size_t srcSize) {
-    const size_t maxNbSeq = (srcSize / ZSTD_MINMATCH_MIN) + 1;
-    const size_t maxNbDelims = (srcSize / ZSTD_BLOCKSIZE_MAX_MIN) + 1;
-    return maxNbSeq + maxNbDelims;
-}
+/* ZSTD_sequenceBound() lives in rust/src/zstd_compress_api.rs. */
 
 size_t ZSTD_generateSequences(ZSTD_CCtx* zc, ZSTD_Sequence* outSeqs,
                               size_t outSeqsSize, const void* src, size_t srcSize)
@@ -3542,21 +3538,7 @@ size_t ZSTD_generateSequences(ZSTD_CCtx* zc, ZSTD_Sequence* outSeqs,
     return zc->seqCollector.seqIndex;
 }
 
-size_t ZSTD_mergeBlockDelimiters(ZSTD_Sequence* sequences, size_t seqsSize) {
-    size_t in = 0;
-    size_t out = 0;
-    for (; in < seqsSize; ++in) {
-        if (sequences[in].offset == 0 && sequences[in].matchLength == 0) {
-            if (in != seqsSize - 1) {
-                sequences[in+1].litLength += sequences[in].litLength;
-            }
-        } else {
-            sequences[out] = sequences[in];
-            ++out;
-        }
-    }
-    return out;
-}
+/* ZSTD_mergeBlockDelimiters() lives in rust/src/zstd_compress_api.rs. */
 
 /* Unrolled loop to read four size_ts of input at a time. Returns 1 if is RLE, 0 if not. */
 static int ZSTD_isRLE(const BYTE* src, size_t length) {