Audit and update code examples for new filter validation and prefix requirements (PR #1291) #1307

The recent filter validation changes in PR #1291 require:

• All user metadata fields in filters to be explicitly prefixed with m. or metadata.
• Filters with unknown or unqualified fields to raise errors (previously ignored)

Please review the following for possible updates:

• All code examples under examples/ that demonstrate filter_dict/query parameters, especially examples that construct or send filters to the backend.
  • Update example code to use m. prefix wherever required by the new backend validation.
  • Correct any example documentation, comments, or sample input/output as needed.
• Add clarifying comments about field prefixing in all relevant places.

Reference: PR #1291 and Documentation Update Issue