feat(compress): move workspace size aggregation to Rust

Keep all context-sensitive workspace sizing in C, including intermediate
allocation calculations, match-state and LDM sizing, error propagation, and
diagnostics. Move only the final nine-component neededSpace aggregation
behind a scalar Rust ABI helper so its size_t wrapping behavior is explicit
and independently tested.

Test Plan:
- `cargo clippy --manifest-path rust/Cargo.toml --no-default-features --features compression` -- passed before and after formatting.
- The same command with `--benches` and `--tests` -- passed before and after formatting.
- `cargo +nightly fmt --manifest-path rust/Cargo.toml` -- passed.
- `cargo test --manifest-path rust/Cargo.toml --no-default-features --features compression zstd_compress` -- 186 passed.
- `make -B -C lib -j2 lib` -- passed.
- `make -C tests test-rust-lib-smoke` -- passed.
- `tests/fuzzer -s4560 -t56 -i57 -v` -- passed.
- `make -C tests -j2 test-zstream` -- 84 named tests and 6,536 plus 7,961 randomized cases passed; the existing unterminated-string warning remains.
- `git diff --cached --check` -- passed.

lib/compress/zstd_compress.c

@@ -92,6 +92,15 @@ size_t ZSTD_rust_sizeofLocalDict(int dictBufferPresent, size_t dictSize,
                                  size_t cdictSize);
 size_t ZSTD_rust_sizeofCCtx(size_t objectSize, size_t workspaceSize,
                             size_t localDictSize, size_t mtctxSize);
+size_t ZSTD_rust_estimateWorkspaceSize(size_t cctxSpace,
+                                       size_t tmpWorkSpace,
+                                       size_t blockStateSpace,
+                                       size_t ldmSpace,
+                                       size_t ldmSeqSpace,
+                                       size_t matchStateSize,
+                                       size_t tokenSpace,
+                                       size_t bufferSpace,
+                                       size_t externalSeqSpace);
 ZSTD_inBuffer ZSTD_rust_inBufferForEndFlush(int inBufferMode,
                                             const void* expectedSrc,
                                             size_t expectedSize,
@@ -1284,16 +1293,9 @@ static size_t ZSTD_estimateCCtxSize_usingCCtxParams_internal(
         ? ZSTD_cwksp_aligned64_alloc_size(maxNbExternalSeq * sizeof(ZSTD_Sequence))
         : 0;
 
-    size_t const neededSpace =
-        cctxSpace +
-        tmpWorkSpace +
-        blockStateSpace +
-        ldmSpace +
-        ldmSeqSpace +
-        matchStateSize +
-        tokenSpace +
-        bufferSpace +
-        externalSeqSpace;
+    size_t const neededSpace = ZSTD_rust_estimateWorkspaceSize(
+        cctxSpace, tmpWorkSpace, blockStateSpace, ldmSpace, ldmSeqSpace,
+        matchStateSize, tokenSpace, bufferSpace, externalSeqSpace);
 
     DEBUGLOG(5, "estimate workspace : %u", (U32)neededSpace);
     return neededSpace;