fix(memory): wrap boto3 clients in context-isolating proxy to silence OTel detach errors

[citizen204]

Problem

When MemoryClient is used inside an asyncio application with aws-opentelemetry-distro (or any OTel boto3 auto-instrumentation), every data-plane or control-plane call emits an ERROR-level log:

ERROR [opentelemetry.context] Failed to detach context
ValueError: Token was created in a different Context

This happens because the OTel boto3 instrumentation calls context.attach() before the API call and context.detach() after. Python's ContextVar.reset() raises ValueError when the token was created in a different execution context -- which occurs when the SDK is used from an asyncio task that inherited OTel context from a parent task, or when a ThreadPoolExecutor worker crosses await boundaries.

At scale (many concurrent agents, AgentCoreMemorySessionManager with asyncio.to_thread()), this fills CloudWatch with spurious ERROR entries that obscure real failures.

Fix

Added _ContextIsolatingProxy -- a thin wrapper around a boto3 client that runs each method call inside contextvars.copy_context().run(). This creates an isolated context snapshot so the OTel attach/detach pair is always contained within the same context, making ContextVar.reset() succeed.

Both gmdp_client (data plane) and gmcp_client (control plane) are wrapped at construction time in MemoryClient.__init__. This fixes every call site -- including direct self.gmdp_client.create_event(...) calls in session_manager.py -- without per-call changes.

The proxy exposes meta directly (for meta.region_name logging) and wraps all callable attributes; non-callable attributes are returned as-is.

Changes

• src/bedrock_agentcore/memory/client.py:
  • Added import contextvars
  • Added _ContextIsolatingProxy class (27 lines, before MemoryClient)
  • Wrapped gmdp_client and gmcp_client with the proxy in __init__

Fixes #456