* feat(iam): implement ListUserPolicies API action (#8987)
Add ListUserPolicies support to both embedded and standalone IAM servers,
resolving the NotImplemented error when calling `aws iam list-user-policies`.
* fix: address review feedback for ListUserPolicies
- Add handleImplicitUsername for ListUserPolicies in both IAM servers
so omitting UserName defaults to the calling user (Gemini review)
- Assert synthetic policy name in unit test (CodeRabbit)
- Use require.True for error type assertion in integration test (CodeRabbit)
* Add AWS IAM integration tests and refactor admin authorization
- Added AWS IAM management integration tests (User, AccessKey, Policy)
- Updated test framework to support IAM client creation with JWT/OIDC
- Refactored s3api authorization to be policy-driven for IAM actions
- Removed hardcoded role name checks for admin privileges
- Added new tests to GitHub Actions basic test matrix
* test(s3/iam): add UpdateUser and UpdateAccessKey tests and fix nil pointer dereference
* feat(s3api): add DeletePolicy and update tests with cleanup logic
* test(s3/iam): use t.Cleanup for managed policy deletion in CreatePolicy test