community[patch]: vectorstores import update (#21169)

Issue: we have several helper functions to import third-party libraries
like lancedb.import_lancedb in
[community.vectorstores](https://api.python.langchain.com/en/latest/vectorstores/langchain_community.vectorstores.lancedb.import_lancedb.html#langchain_community.vectorstores.lancedb.import_lancedb).
And we have core.utils.utils.guard_import that works exactly for this
purpose.
The import_<package> functions work inconsistently and rather be private
functions.
Change: replaced these functions with the guard_import function.

Related to #21133

libs/community/langchain_community/vectorstores/usearch.py

@@ -5,6 +5,7 @@ from typing import Any, Dict, Iterable, List, Optional, Tuple
 import numpy as np
 from langchain_core.documents import Document
 from langchain_core.embeddings import Embeddings
+from langchain_core.utils import guard_import
 from langchain_core.vectorstores import VectorStore
 
 from langchain_community.docstore.base import AddableMixin, Docstore
@@ -15,14 +16,7 @@ def dependable_usearch_import() -> Any:
     """
     Import usearch if available, otherwise raise error.
     """
-    try:
-        import usearch.index
-    except ImportError:
-        raise ImportError(
-            "Could not import usearch python package. "
-            "Please install it with `pip install usearch` "
-        )
-    return usearch.index
+    return guard_import("usearch.index")
 
 
 class USearch(VectorStore):
@@ -170,7 +164,7 @@ class USearch(VectorStore):
             documents.append(Document(page_content=text, metadata=metadata))
 
         docstore = InMemoryDocstore(dict(zip(ids, documents)))
-        usearch = dependable_usearch_import()
+        usearch = guard_import("usearch.index")
         index = usearch.Index(ndim=len(embeddings[0]), metric=metric)
         index.add(np.array(ids), np.array(embeddings))
         return cls(embedding, index, docstore, ids.tolist())