Add two tests in TestTagStoreSerialisation class that verify the new tag_store JSON serialisation format for non-empty tag stores: - test_non_empty_tag_store_serialization: Single entry {0: (2, 1)} - test_multiple_entries_tag_store_serialization: Multiple entries with different act_id values and lane assignments These tests verify that: - tag_store entries are serialized as {"act_id_str": {"frame_id": N, "lane": M}} - lane_count is present in the PE state JSON - All entries are correctly converted to string keys and nested objects Fixes: No test asserts the new tag_store JSON serialisation format for non-empty tag stores (Phase 5 code review issue)