fix: remove NotRequried as it is supported only in python 3.11

[glsukki]

The NotRequired construct from typing is supported only in Python 3.11.

To avoid breaking dependencies which use a lower version (Python <3.11) - replacing the NotRequired with Optional for the EventMetadataFilter.right field.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 58.33333% with 5 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@1bdddf6). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
src/bedrock_agentcore/memory/models/filters.py	54.54%	5 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #125   +/-   ##
=======================================
  Coverage        ?   89.54%           
=======================================
  Files           ?       24           
  Lines           ?     2391           
  Branches        ?      341           
=======================================
  Hits            ?     2141           
  Misses          ?      146           
  Partials        ?      104           

Flag	Coverage Δ
unittests	89.54% <58.33%> (?)

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