refactor(FilterStructToMap): change return type to use OrderedMap

[hanXen]

Resolves #679

Summary

This PR refactors FilterStructToMap to return a *mapsutil.OrderedMap[string, any] instead of a standard map[string]any.

The current function's use of a standard map results in non-deterministic key order when marshaled to JSON. By returning an OrderedMap, we leverage its custom MarshalJSON method to preserve the original struct field order, ensuring consistent output for downstream tools.

Impact Assessment

This change has a limited impact surface.

• naabu (fix(output): ensure -eof completely omit fields from JSON output naabu#1546): No code changes are required. The existing implementation works seamlessly with the new return type.
• katana (feat(output): Add -eof and -lof flags for JSON output filtering katana#1390): Requires a minor update: standard map operations are replaced with the corresponding OrderedMap methods (e.g., m["key"] → m.Get("key")).

Overall, the modification makes the utility more robust while minimizing adjustments in dependent projects.