refactor(cli): move LZ4 block-size policy leaf to Rust

Export FIO_LZ4_GetBlockSize_FromBlockId directly from Rust under the existing
caller symbol and remove the redundant C forwarding wrapper. Preserve the
block-ID formula and cover its boundary values in the focused Rust test.

Test Plan:
- worker capped nightly rustfmt check
- worker git diff --check
- full serial capped native and upstream suites to run at the next parent gate

programs/fileio.c

@@ -588,7 +588,7 @@ int FIO_rust_decompressLz4Frame(
 
 void FIO_rust_displayCompressionParameters(const FIO_prefs_t* prefs);
 #ifdef ZSTD_LZ4COMPRESS
-int FIO_rust_LZ4_GetBlockSize_FromBlockId(int id);
+int FIO_LZ4_GetBlockSize_FromBlockId(int id);
 #endif
 
 
@@ -2228,11 +2228,6 @@ FIO_compressLzmaFrame(cRess_t* ress,
 #define LZ4F_max64KB max64KB
 #endif
 
-static int FIO_LZ4_GetBlockSize_FromBlockId (int id)
-{
-    return FIO_rust_LZ4_GetBlockSize_FromBlockId(id);
-}
-
 typedef struct {
     LZ4F_compressionContext_t ctx;
     LZ4F_preferences_t prefs;