Reduce duplicated data and memory consuption by adding copy on writeopts dictionary

Add validation to ensure:- opts is a valid dict-like object- new_value is not None (or handle None case properly)- Better error handling for edge casesThis helps prevent issues in CI environments where test isolationor parallel execution might expose edge cases not seen locally.

The isinstance() check for master_opts() was failing when it returnedan OptsDict instead of a dict. OptsDict is a MutableMapping, not a dictsubclass, so the check `isinstance(mopts, dict)` would fail and causethe code to incorrectly use default file_roots (/srv/salt) instead ofthe actual configured file_roots.This caused 175 test failures in CI where tests would return emptyresults because the file client couldn't find the test files.Fixed by checking for both dict and Mapping types:    isinstance(mopts, (dict, Mapping))🤖 Generated with [Claude Code](https://claude.com/claude-code)Co-Authored-By: Claude <noreply@anthropic.com>