fix(text-embeddings): compare text_encoder_norm_type case-insensitively

[James D. Finlon (jim-finlon)]

Summary

• compare string config values case-insensitively for dual-aggregate text embedding config validation
• keep non-string expected values strict so boolean checks do not become string-coercion checks
• add a pytest covering both 'per_token_rms' and 'PER_TOKEN_RMS'

Context

This covers the same distilled checkpoint failure mode as #478, but includes pytest coverage and keeps non-string config validation strict.

Validation

• python -m pytest --rootdir=/tmp/comfyui-ltxvideo-dna-pr.bRrNmp/tests /tmp/comfyui-ltxvideo-dna-pr.bRrNmp/tests/test_text_embeddings_config_validation.py -q
• PYTHONPATH=/tmp/dna-black-24.4.2 python -m black --check text_embeddings_connectors.py tests/test_text_embeddings_config_validation.py