community[minor]: add bedrock anthropic callback for token usage counting (#19864)

**Description:** add bedrock anthropic callback for token usage
counting, consulted openai callback.

---------

Co-authored-by: Massimiliano Pronesti <massimiliano.pronesti@gmail.com>

libs/community/langchain_community/callbacks/manager.py

@@ -10,6 +10,9 @@ from typing import (
 
 from langchain_core.tracers.context import register_configure_hook
 
+from langchain_community.callbacks.bedrock_anthropic_callback import (
+    BedrockAnthropicTokenUsageCallbackHandler,
+)
 from langchain_community.callbacks.openai_info import OpenAICallbackHandler
 from langchain_community.callbacks.tracers.comet import CometTracer
 from langchain_community.callbacks.tracers.wandb import WandbTracer
@@ -19,7 +22,10 @@ logger = logging.getLogger(__name__)
 openai_callback_var: ContextVar[Optional[OpenAICallbackHandler]] = ContextVar(
     "openai_callback", default=None
 )
-wandb_tracing_callback_var: ContextVar[Optional[WandbTracer]] = ContextVar(  # noqa: E501
+bedrock_anthropic_callback_var: (ContextVar)[
+    Optional[BedrockAnthropicTokenUsageCallbackHandler]
+] = ContextVar("bedrock_anthropic_callback", default=None)
+wandb_tracing_callback_var: ContextVar[Optional[WandbTracer]] = ContextVar(
     "tracing_wandb_callback", default=None
 )
 comet_tracing_callback_var: ContextVar[Optional[CometTracer]] = ContextVar(  # noqa: E501
@@ -27,6 +33,7 @@ comet_tracing_callback_var: ContextVar[Optional[CometTracer]] = ContextVar(  # n
 )
 
 register_configure_hook(openai_callback_var, True)
+register_configure_hook(bedrock_anthropic_callback_var, True)
 register_configure_hook(
     wandb_tracing_callback_var, True, WandbTracer, "LANGCHAIN_WANDB_TRACING"
 )
@@ -53,6 +60,27 @@ def get_openai_callback() -> Generator[OpenAICallbackHandler, None, None]:
     openai_callback_var.set(None)
 
 
+@contextmanager
+def get_bedrock_anthropic_callback() -> (
+    Generator[BedrockAnthropicTokenUsageCallbackHandler, None, None]
+):
+    """Get the Bedrock anthropic callback handler in a context manager.
+    which conveniently exposes token and cost information.
+
+    Returns:
+        BedrockAnthropicTokenUsageCallbackHandler:
+            The Bedrock anthropic callback handler.
+
+    Example:
+        >>> with get_bedrock_anthropic_callback() as cb:
+        ...     # Use the Bedrock anthropic callback handler
+    """
+    cb = BedrockAnthropicTokenUsageCallbackHandler()
+    bedrock_anthropic_callback_var.set(cb)
+    yield cb
+    bedrock_anthropic_callback_var.set(None)
+
+
 @contextmanager
 def wandb_tracing_enabled(
     session_name: str = "default",