Fix DynamicCommunitySelection type mismatch for children IDs

[majiayu000]

Summary

• Fix type mismatch in DynamicCommunitySelection.select() where children IDs (integers) were not matching string report keys
• Convert child to string before checking membership in self.reports

Problem

In dynamic_community_selection.py, the children list may contain integers while self.reports keys are strings. This causes if child in self.reports to always return False, skipping all child communities during dynamic selection.

Solution

Convert children IDs to strings using str(child) before checking membership and appending to communities_to_rate.

Test Plan

• Added unit tests for both integer and string children scenarios
• All existing unit tests pass
• Static checks (ruff, pyright) pass

Fixes #2004

[gaudyb]

Implemented in PR #2159 using this logic and #2124 PRs. Thank you!