community: callbacks guard_imports (#21173)

Issue: we have several helper functions to import third-party libraries
like import_uptrain in
[community.callbacks](https://api.python.langchain.com/en/latest/callbacks/langchain_community.callbacks.uptrain_callback.import_uptrain.html#langchain_community.callbacks.uptrain_callback.import_uptrain).
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/callbacks/fiddler_callback.py

@@ -4,6 +4,7 @@ from uuid import UUID
 
 from langchain_core.callbacks import BaseCallbackHandler
 from langchain_core.outputs import LLMResult
+from langchain_core.utils import guard_import
 
 from langchain_community.callbacks.utils import import_pandas
 
@@ -54,14 +55,7 @@ _dataset_dict = {
 
 def import_fiddler() -> Any:
     """Import the fiddler python package and raise an error if it is not installed."""
-    try:
-        import fiddler
-    except ImportError:
-        raise ImportError(
-            "To use fiddler callback handler you need to have `fiddler-client`"
-            "package installed. Please install it with `pip install fiddler-client`"
-        )
-    return fiddler
+    return guard_import("fiddler", pip_name="fiddler-client")
 
 
 # First, define custom callback handler implementations