fix: honor embedding api_key from config dict across providers

[lfnovo]

Summary

• fix API key resolution in embedding providers to honor config-resolved values before env fallback
• apply the fix to OpenAI, Google, Jina, and Voyage embedding providers
• bump package version to 2.19.1
• add changelog entry for the fix
• add regression tests for config={"api_key": "..."} initialization paths

Why

Some users passed API keys via config (e.g. through factory methods) and still got API key not found in embedding providers due to provider-specific init overriding resolved credentials.

Validation

• uv run pytest -q tests/providers/embedding/test_embedding_providers.py -k "openai_initialization_with_config_api_key or google_initialization_with_config_api_key"
• uv run pytest -q tests/providers/embedding/test_jina.py -k "config_api_key or init_with_api_key or init_with_env_var or init_without_api_key"
• uv run pytest -q tests/providers/embedding/test_voyage_provider.py -k "config_api_key or init_with_api_key or init_with_env_api_key or init_without_api_key"

[cubic-dev-ai]

No issues found across 9 files