feat(compress): move simple strategy selection into Rust

The Rust simple-compression entry points already owned the dispatch, but
ZSTD_rust_compressCCtxStrategy still called the C parameter cascade to decide
whether a fast Rust frame path was safe. That left a small policy leaf in the
C implementation and made the dispatch boundary harder to test in isolation.

Implement the helper in Rust by using the existing Rust table-selection and
C-parameter-adjustment functions with the same source-size, dictionary-mode,
and automatic-adjustment inputs as the C code. Leave only the C ABI declaration
and add tests for the table thresholds, default-level behavior, and negative
fast-level behavior. The private context reset and fallback compression paths
remain unchanged.

Test Plan:
- `cargo test --manifest-path rust/Cargo.toml --lib zstd_compress --
  --test-threads=1` -- passed (234 tests).
- `cargo clippy --manifest-path rust/Cargo.toml --lib -- -D warnings` -- passed.
- `cargo +nightly fmt --manifest-path rust/Cargo.toml -- --check` -- passed.
- `make -B -C lib -j2 lib` -- passed.
- `make -C tests -j2 test-rust-lib-smoke` -- passed.
- Full-target clippy remains blocked by pre-existing test-only
  `manual_repeat_n` and `manual_dangling_ptr` warnings outside this seam.

lib/compress/zstd_compress.c

@@ -3849,13 +3849,6 @@ size_t ZSTD_compress_usingDict(ZSTD_CCtx* cctx,
 
 /* The Rust simple API still needs the C-owned context reset, but does not
  * cross the private context layout. */
-int ZSTD_rust_compressCCtxStrategy(size_t srcSize, int compressionLevel)
-{
-    ZSTD_parameters const params = ZSTD_getParams_internal(
-            compressionLevel, srcSize, 0, ZSTD_cpm_noAttachDict);
-    return (int)params.cParams.strategy;
-}
-
 size_t ZSTD_rust_resetCCtxForSimpleCompression(void* cctx)
 {
     return ZSTD_CCtx_reset((ZSTD_CCtx*)cctx, ZSTD_reset_session_and_parameters);