refactor(compress): expose block policy leaves from Rust

Export ZSTD_useTargetCBlockSize and ZSTD_blockSplitterEnabled directly from
Rust under their existing caller symbols. Remove the redundant C forwarding
wrappers while preserving diagnostics, ABI signatures, and parameter layout.

Test Plan:
- worker capped format, C syntax, and diff checks
- parent capped root clippy and native build
- parent capped upstream make -j1 -C tests test
- parent capped CLI clippy and tests

rust/src/zstd_compress_params_api.rs

@@ -363,9 +363,7 @@ unsafe fn use_target_c_block_size(cctx_params: *const ZSTD_CCtx_params) -> c_int
 }
 
 #[no_mangle]
-pub unsafe extern "C" fn ZSTD_rust_useTargetCBlockSize(
-    cctx_params: *const ZSTD_CCtx_params,
-) -> c_int {
+pub unsafe extern "C" fn ZSTD_useTargetCBlockSize(cctx_params: *const ZSTD_CCtx_params) -> c_int {
     unsafe { use_target_c_block_size(cctx_params) }
 }
 
@@ -377,9 +375,7 @@ unsafe fn block_splitter_enabled(cctx_params: *mut ZSTD_CCtx_params) -> c_int {
 }
 
 #[no_mangle]
-pub unsafe extern "C" fn ZSTD_rust_blockSplitterEnabled(
-    cctx_params: *mut ZSTD_CCtx_params,
-) -> c_int {
+pub unsafe extern "C" fn ZSTD_blockSplitterEnabled(cctx_params: *mut ZSTD_CCtx_params) -> c_int {
     unsafe { block_splitter_enabled(cctx_params) }
 }
 
@@ -1344,10 +1340,10 @@ mod tests {
         let params = storage.as_mut_ptr();
         unsafe {
             (*params).targetCBlockSize = 0;
-            assert_eq!(ZSTD_rust_useTargetCBlockSize(params), 0);
+            assert_eq!(ZSTD_useTargetCBlockSize(params), 0);
 
             (*params).targetCBlockSize = 1;
-            assert_eq!(ZSTD_rust_useTargetCBlockSize(params), 1);
+            assert_eq!(ZSTD_useTargetCBlockSize(params), 1);
         }
     }
 
@@ -1357,10 +1353,10 @@ mod tests {
         let params = storage.as_mut_ptr();
         unsafe {
             (*params).postBlockSplitter = ZSTD_RUST_PS_ENABLE;
-            assert_eq!(ZSTD_rust_blockSplitterEnabled(params), 1);
+            assert_eq!(ZSTD_blockSplitterEnabled(params), 1);
 
             (*params).postBlockSplitter = PS_DISABLE;
-            assert_eq!(ZSTD_rust_blockSplitterEnabled(params), 0);
+            assert_eq!(ZSTD_blockSplitterEnabled(params), 0);
         }
     }