feat(fileio): move filename collision checks to Rust

Implement basename extraction, bytewise sorting, collision reporting, and allocation failure handling in the Rust fileio preferences module. Keep programs/fileio.c as the stable ABI shim and preserve non-UTF-8 filenames without lossy conversion.

Test Plan:

- cargo test --manifest-path rust/cli/Cargo.toml --no-default-features --features cli,compression,decompression

- cargo clippy --manifest-path rust/cli/Cargo.toml --all-targets --no-default-features --features cli,compression,decompression

- make -B -C tests -j2 test-cli-tests

- git diff --cached --check

programs/fileio.c

@@ -306,6 +306,7 @@ static int FIO_shouldDisplayMultipleFileSummary(FIO_ctx_t const* fCtx)
 
 /* These symbols are implemented by rust/src/fileio_prefs.rs.  The declarations
  * in fileio.h remain the C ABI shims while all actual file I/O stays here. */
+int FIO_rust_checkFilenameCollisions(const char** filenameTable, unsigned nbFiles);
 
 
 /*-*************************************
@@ -678,35 +679,7 @@ static void FIO_initDict(FIO_Dict_t* dict, const char* fileName, FIO_prefs_t* co
  * Checks for and warns if there are any files that would have the same output path
  */
 int FIO_checkFilenameCollisions(const char** filenameTable, unsigned nbFiles) {
-    const char **filenameTableSorted, *prevElem, *filename;
-    unsigned u;
-
-    filenameTableSorted = (const char**) malloc(sizeof(char*) * nbFiles);
-    if (!filenameTableSorted) {
-        DISPLAYLEVEL(1, "Allocation error during filename collision checking \n");
-        return 1;
-    }
-
-    for (u = 0; u < nbFiles; ++u) {
-        filename = strrchr(filenameTable[u], PATH_SEP);
-        if (filename == NULL) {
-            filenameTableSorted[u] = filenameTable[u];
-        } else {
-            filenameTableSorted[u] = filename+1;
-        }
-    }
-
-    qsort((void*)filenameTableSorted, nbFiles, sizeof(char*), UTIL_compareStr);
-    prevElem = filenameTableSorted[0];
-    for (u = 1; u < nbFiles; ++u) {
-        if (strcmp(prevElem, filenameTableSorted[u]) == 0) {
-            DISPLAYLEVEL(2, "WARNING: Two files have same filename: %s\n", prevElem);
-        }
-        prevElem = filenameTableSorted[u];
-    }
-
-    free((void*)filenameTableSorted);
-    return 0;
+    return FIO_rust_checkFilenameCollisions(filenameTable, nbFiles);
 }
 
 char* UTIL_createFilenameFromOutDir(const char* path, const char* outDirName,