fix(python): expose register function in embeddings module (#2544)

## Summary
Fixes #2541

**Problem**: The `register` function was not accessible via `from
lancedb.embeddings import register` as documented, causing ImportError
for users trying to create custom embedding functions.

**Solution**: Added `register` to the exports in
`python/lancedb/embeddings/__init__.py` to match the documented API and
follow the same pattern as other registry functions (`get_registry`,
`EmbeddingFunctionRegistry`).

**Root Cause**: The function existed in `lancedb.embeddings.registry`
but wasn't exposed through the main embeddings module interface.

## Changes
- Add `register` to imports in
`/python/python/lancedb/embeddings/__init__.py`

## Test Plan
- [x] Verified `from lancedb.embeddings import register` works as
documented
- [x] Confirmed existing embedding tests pass
- [x] Checked that the fix follows existing patterns (same as
`get_registry`)
- [x] Validated linting and formatting passes

## References
Fixes #2541

python/python/lancedb/embeddings/__init__.py

@@ -11,7 +11,7 @@ from .instructor import InstructorEmbeddingFunction
 from .ollama import OllamaEmbeddings
 from .open_clip import OpenClipEmbeddings
 from .openai import OpenAIEmbeddings
-from .registry import EmbeddingFunctionRegistry, get_registry
+from .registry import EmbeddingFunctionRegistry, get_registry, register
 from .sentence_transformers import SentenceTransformerEmbeddings
 from .gte import GteEmbeddings
 from .transformers import TransformersEmbeddingFunction, ColbertEmbeddings