fix(strands): ban experimental import

[Hweinstock]

Problem

The AgentCore Python SDK imported APIs from strands.experimental, creating a dependency on unstable Strands interfaces.

Solution

• Remove experimental Strands imports and their obsolete Bidi-specific hooks/tests.
• Add Ruff TID251 configuration banning strands.experimental imports.

Verification

• unit tests pass: 185 passed.
• Memory session-manager integration tests pass: 12 passed in 10m28s

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (main@3a6496e). Learn more about missing BASE report.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #686   +/-   ##
=======================================
  Coverage        ?   89.53%           
=======================================
  Files           ?      124           
  Lines           ?    10719           
  Branches        ?     1675           
=======================================
  Hits            ?     9597           
  Misses          ?      734           
  Partials        ?      388           

Flag	Coverage Δ
unittests	89.53% <100.00%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[agentcore-devx-automation]

Claude Security Review: no high-confidence findings. (run)