fix(memory): use current Strands bidi session hooks

[pgrayy]

Issue #, if available:

N/A

Description of changes:

Importing AgentCoreMemorySessionManager fails with Strands 1.56.0 because it references bidi hook events removed in strands-agents/harness-sdk#4280. Use the shared initialization and message hooks for both Agent and BidiAgent, and use BidiAgentStopEvent to save state when a bidi session stops. Keep initialization synchronous and offload persistence callbacks when async_mode=True.

Update the agent annotations to LocalAgent, migrate the existing hook-registration test, and raise the minimum strands-agents version to 1.56.0.

Validation:

• All pre-commit checks and the Bandit security scan passed.
• The full test suite with coverage passed in the locked Python 3.10 development environment (91% coverage). The focused session-manager suite also passed on Python 3.13 (182 tests).
• Five existing live AWS integration tests passed, covering initialization, conversation persistence, batching, and session restoration.
• Two one-off bidi checks passed against live AgentCore storage with a scripted model. These exercised public start, send, receive, and stop calls in both callback modes, including message restoration and state saved on stop.

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@9f31042). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
...ore/memory/integrations/strands/session_manager.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #664   +/-   ##
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  Coverage        ?   89.51%           
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  Files           ?      123           
  Lines           ?    10700           
  Branches        ?     1677           
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  Hits            ?     9578           
  Misses          ?      734           
  Partials        ?      388           

Flag	Coverage Δ
unittests	89.51% <80.00%> (?)

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