added return_fields function, attempting to optionally limit fields r… (#633)

Add Django-style .values() and .only() methods to return partial results:
- .values() returns all fields as dicts
- .values('field1', 'field2') returns specific fields as dicts
- Uses Redis RETURN clause for efficient field projection
- Similar with .only(), except returns partial model objects
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Co-authored-by: savynorem <savannah.norem@redis.com>
Co-authored-by: Brian Sam-Bodden <bsb@redis.com>
Co-authored-by: Andrew Brookins <a.m.brookins@gmail.com>
Co-authored-by: Claude <noreply@anthropic.com>

Author: 5 people