refactor(cli): move --list stdin predicate to Rust

The --list stdin callback was a stateless string predicate: it ignored its
opaque context and compared the input name with the fixed stdin marker. Move
that callback under its existing caller symbol into the Rust CLI archive, so
C no longer owns this policy leaf. The Rust implementation preserves the
callback ABI and returns the same 1/0 result for the marker and ordinary
names. File opening, frame parsing, diagnostics, human-readable formatting,
private file-info storage, and list orchestration remain C-owned. The optional
codec-version helpers remain untouched because their build-time library
configuration is not propagated to the Rust archive.

Test Plan:
- `clang -fsyntax-only -Iprograms -Ilib -Ilib/common -Ilib/compress -Ilib/decompress -Ilib/dictBuilder programs/fileio.c` -- passed.
- `rustfmt --edition 2021 --check --config skip_children=true rust/cli/src/lib.rs` -- passed.
- `git diff --check` and `git diff --cached --check` -- passed.
- Cargo, clippy, native builds, and upstream tests were not run per the explicit no-heavy-command constraint.

programs/fileio.c

@@ -4998,12 +4998,8 @@ FIO_listFile(const char* inFileName, int displayLevel,
     }
 }
 
-static int
-FIO_listFileIsStdin(void* opaque, const char* fileName)
-{
-    (void)opaque;
-    return !strcmp(fileName, stdinmark);
-}
+/* Rust owns this stateless --list input-name predicate. */
+int FIO_listFileIsStdin(void* opaque, const char* fileName);
 
 static void
 FIO_listFileDisplayStdinError(void* opaque)

rust/cli/src/lib.rs

@@ -29,3 +29,41 @@ mod zstd_cli;
 #[cfg(feature = "cli")]
 #[path = "../../src/zstdcli_trace.rs"]
 mod zstdcli_trace;
+
+#[cfg(feature = "cli")]
+use std::ffi::c_void;
+#[cfg(feature = "cli")]
+use std::os::raw::{c_char, c_int};
+
+/// Match the C `--list` stdin callback without crossing any file-I/O state.
+#[cfg(feature = "cli")]
+#[no_mangle]
+pub unsafe extern "C" fn FIO_listFileIsStdin(
+    _opaque: *mut c_void,
+    file_name: *const c_char,
+) -> c_int {
+    assert!(!file_name.is_null());
+    c_int::from(unsafe { libc::strcmp(file_name, c"/*stdin*\\".as_ptr()) == 0 })
+}
+
+#[cfg(all(test, feature = "cli"))]
+mod tests {
+    use super::FIO_listFileIsStdin;
+    use std::ffi::CString;
+    use std::ptr;
+
+    #[test]
+    fn list_stdin_callback_matches_only_the_stdin_marker() {
+        let stdin_name = CString::new("/*stdin*\\").unwrap();
+        let ordinary_name = CString::new("input.zst").unwrap();
+
+        assert_eq!(
+            unsafe { FIO_listFileIsStdin(ptr::null_mut(), stdin_name.as_ptr()) },
+            1
+        );
+        assert_eq!(
+            unsafe { FIO_listFileIsStdin(ptr::null_mut(), ordinary_name.as_ptr()) },
+            0
+        );
+    }
+}