feat(params): move context-free getters into Rust

Compression-parameter table selection and adjustment were already implemented
as Rust leaves, but the internal and public ZSTD_getCParams/ZSTD_getParams
helpers still assembled those results in the C translation unit. That left
source-size and dictionary-mode policy duplicated at the C/Rust boundary.

Add Rust implementations for the internal and public getter policies. The
internal helpers preserve a zero source size as a known empty input, while the
public helpers retain the API rule that zero means unknown. The C side keeps
only the build-specific exclusion-mask construction and thin ABI adapters, so
reduced builds continue to select the same available strategy cascade.

Test Plan:
- `cargo test --manifest-path rust/Cargo.toml --lib -- --test-threads=1`
  -- passed (411 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.
- Focused tests cover public zero-to-unknown translation, internal zero
  semantics, default frame parameters, and dictionary attachment modes.

lib/compress/zstd_compress.c

@@ -148,6 +148,18 @@ ZSTD_compressionParameters
 ZSTD_rust_params_adjustCParams(ZSTD_compressionParameters cParams, U64 srcSize,
                                size_t dictSize, int mode,
                                int useRowMatchFinder);
+ZSTD_compressionParameters ZSTD_rust_params_getCParamsInternal(
+        int compressionLevel, U64 srcSizeHint, size_t dictSize, int mode,
+        U32 exclusionMask);
+ZSTD_parameters ZSTD_rust_params_getParamsInternal(
+        int compressionLevel, U64 srcSizeHint, size_t dictSize, int mode,
+        U32 exclusionMask);
+ZSTD_compressionParameters ZSTD_rust_params_getCParams(
+        int compressionLevel, U64 srcSizeHint, size_t dictSize,
+        U32 exclusionMask);
+ZSTD_parameters ZSTD_rust_params_getParams(
+        int compressionLevel, U64 srcSizeHint, size_t dictSize,
+        U32 exclusionMask);
 ZSTD_compressionParameters ZSTD_rust_params_applyStrategyExclusions(
         ZSTD_compressionParameters cParams, U32 exclusionMask);
 ZSTD_compressionParameters ZSTD_rust_params_getCParamsFromCCtxParams(
@@ -5697,12 +5709,9 @@ static void ZSTD_dedicatedDictSearch_revertCParams(
  *  Note: `mode` controls how we treat the `dictSize`. See docs for `ZSTD_CParamMode_e`. */
 static ZSTD_compressionParameters ZSTD_getCParams_internal(int compressionLevel, unsigned long long srcSizeHint, size_t dictSize, ZSTD_CParamMode_e mode)
 {
-    /* Table selection is context-free and lives in Rust; the adjustment step
-     * stays behind ZSTD_adjustCParams_internal() so this build's strategy
-     * cascade applies. */
-    ZSTD_compressionParameters const cp = ZSTD_rust_params_selectCParams(
-            compressionLevel, srcSizeHint, dictSize, (int)mode);
-    return ZSTD_adjustCParams_internal(cp, srcSizeHint, dictSize, mode, ZSTD_ps_auto);
+    return ZSTD_rust_params_getCParamsInternal(
+            compressionLevel, srcSizeHint, dictSize, (int)mode,
+            ZSTD_getCParamsExclusionMask());
 }
 
 /*! ZSTD_getCParams() :
@@ -5710,8 +5719,9 @@ static ZSTD_compressionParameters ZSTD_getCParams_internal(int compressionLevel,
  *  Size values are optional, provide 0 if not known or unused */
 ZSTD_compressionParameters ZSTD_getCParams(int compressionLevel, unsigned long long srcSizeHint, size_t dictSize)
 {
-    if (srcSizeHint == 0) srcSizeHint = ZSTD_CONTENTSIZE_UNKNOWN;
-    return ZSTD_getCParams_internal(compressionLevel, srcSizeHint, dictSize, ZSTD_cpm_unknown);
+    return ZSTD_rust_params_getCParams(
+            compressionLevel, srcSizeHint, dictSize,
+            ZSTD_getCParamsExclusionMask());
 }
 
 /*! ZSTD_getParams() :
@@ -5721,9 +5731,10 @@ ZSTD_compressionParameters ZSTD_getCParams(int compressionLevel, unsigned long l
 static ZSTD_parameters
 ZSTD_getParams_internal(int compressionLevel, unsigned long long srcSizeHint, size_t dictSize, ZSTD_CParamMode_e mode)
 {
-    ZSTD_compressionParameters const cParams = ZSTD_getCParams_internal(compressionLevel, srcSizeHint, dictSize, mode);
     DEBUGLOG(5, "ZSTD_getParams (cLevel=%i)", compressionLevel);
-    return ZSTD_rust_params_makeParams(cParams);
+    return ZSTD_rust_params_getParamsInternal(
+            compressionLevel, srcSizeHint, dictSize, (int)mode,
+            ZSTD_getCParamsExclusionMask());
 }
 
 /*! ZSTD_getParams() :
@@ -5732,8 +5743,9 @@ ZSTD_getParams_internal(int compressionLevel, unsigned long long srcSizeHint, si
  *  Fields of `ZSTD_frameParameters` are set to default values */
 ZSTD_parameters ZSTD_getParams(int compressionLevel, unsigned long long srcSizeHint, size_t dictSize)
 {
-    if (srcSizeHint == 0) srcSizeHint = ZSTD_CONTENTSIZE_UNKNOWN;
-    return ZSTD_getParams_internal(compressionLevel, srcSizeHint, dictSize, ZSTD_cpm_unknown);
+    return ZSTD_rust_params_getParams(
+            compressionLevel, srcSizeHint, dictSize,
+            ZSTD_getCParamsExclusionMask());
 }
 
 void ZSTD_registerSequenceProducer(