- Add gemini-embedding-2-preview to supported embedding models
- Support outputDimensionality (768/1536/3072, default 3072) for v2 models
- Support taskType parameter for semantic retrieval optimization
- Add multimodal part builders (buildInlineDataPart, buildFileDataPart)
- Set 8192 token limit for gemini-embedding-2-preview
- Maintain backward compatibility for gemini-embedding-001 (no new fields)
- Add comprehensive test coverage (26 tests)
Closes#42487