volcengine#702)

…cengine#702)

Clean implementation on latest main (post PR volcengine#702 merge):
- Add _parse_param_string() method for key=value parsing
- Enhance _build_extra_body() to support multiple parameters
- Maintain backward compatibility with simple string format
- Update docstrings and examples

Usage:
- Simple: query_param='query' → {'input_type': 'query'}
- Enhanced: query_param='input_type=query,task=search' → {'input_type': 'query', 'task': 'search'}

Supports OpenAI-compatible servers with custom parameters while
maintaining clean integration with PR volcengine#702's is_query API.

* feat: add key=value parameter parsing to OpenAI embedder

Clean implementation on latest main (post PR #702 merge):
- Add _parse_param_string() method for key=value parsing
- Enhance _build_extra_body() to support multiple parameters
- Maintain backward compatibility with simple string format
- Update docstrings and examples

Usage:
- Simple: query_param='query' → {'input_type': 'query'}
- Enhanced: query_param='input_type=query,task=search' → {'input_type': 'query', 'task': 'search'}

Supports OpenAI-compatible servers with custom parameters while
maintaining clean integration with PR #702's is_query API.

* fix: lint issues

…ngine#702 pattern

- GeminiDenseEmbedder: accept query_param/document_param, use is_query
  in embed() and embed_batch() to select task_type at call time
- EmbeddingConfig: add Gemini provider, factory, validation, dimension
- No get_query_embedder/get_document_embedder/_get_contextual_embedder
  (removed in volcengine#702; embed(is_query=True/False) is the pattern)
- Tests use embed(text, is_query=True/False) pattern throughout
- Rebased onto current upstream/main

* feat(gemini): add GeminiDenseEmbedder with is_query routing per #702 pattern

- GeminiDenseEmbedder: accept query_param/document_param, use is_query
  in embed() and embed_batch() to select task_type at call time
- EmbeddingConfig: add Gemini provider, factory, validation, dimension
- No get_query_embedder/get_document_embedder/_get_contextual_embedder
  (removed in #702; embed(is_query=True/False) is the pattern)
- Tests use embed(text, is_query=True/False) pattern throughout
- Rebased onto current upstream/main

* fix(gemini): remove task_type config field, fix conditional import for CI

- Remove task_type from EmbeddingModelConfig (query_param/document_param suffice)
- Wrap GeminiDenseEmbedder import in try/except (google-genai is optional)
- Update tests for removed field