Add Python 3.14 support

[abrookins]

Summary

Add Python 3.14 support to RedisVL.

Changes

• Update requires-python upper bound from <3.14 to <3.15
• Add Programming Language :: Python :: 3.14 classifier
• Add Python 3.14 to the CI test matrix

Testing Strategy

HuggingFace/sentence-transformers tests are skipped on Python 3.14 because the upstream transformers library doesn't fully support Python 3.14 yet.

Affected components (all optional):

• HFTextVectorizer
• HFCrossEncoderReranker
• SemanticRouter (when using default HF vectorizer)
• SemanticMessageHistory (when using HF vectorizer)

Users can still use these features on Python 3.9-3.13, or use alternative vectorizers (OpenAI, Cohere, etc.) on Python 3.14.

Implementation:

• Added SKIP_HF constant in conftest.py to detect Python 3.14+
• Skip HF-dependent test files entirely via pytestmark
• Skip individual HF tests via @pytest.mark.requires_hf marker
• Skip HF parameters in parametrized tests via pytest.param(..., marks=...)

Once transformers adds Python 3.14 support, these skips can be removed.

Additional Fix

Added missing @pytest.mark.requires_api_keys marker to test_default_dtype (pre-existing bug unrelated to this PR).