Fix assessment API drift and stabilize tests

[agasthik]

Issue #, if available:
#42

Description of changes:

Summary

This PR fixes Bedrock assessment issues caused by API drift and missing permissions, updates AgentCore checks for current API shapes, and stabilizes the test suite.

Changes

• Fixed BR-04 false positive by handling Bedrock invocation logging S3 config via bucketName
• Added missing Bedrock Knowledge Base permissions for BR-09
• Fixed BR-12 access-denied handling to report COULD NOT ASSESS
• Patched additional verified Bedrock issues in BR-07 and BR-08
• Updated AgentCore checks for current response shapes and generic resource policy lookups
• Fixed FinServ test import shadowing (app / schema / conftest)
• Added shared test helper modules and cleaned up residual bad patch targets
• Fixed AgentCore tests that were still leaking to live boto3 clients
• Cleaned up Ruff findings in touched files

Validation

• Verified Bedrock behavior against real AWS CLI responses

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[vivekmittal514]

Ran for single and multi account and the reports are fine.