perf: make EventBus subscription removal O(1) via ID→type index

[KrisSimon]

Migrated from GitLab MR !215 (merged)
feature/eventbus-o1-removal-139 → main
Originally created: 2026-03-31
Merged: 2026-04-01
Author: Kris Simon

Summary

• Adds a [UUID: String] side-map (idToType) in SubscriptionStore that records which event-type bucket each subscription belongs to
• remove() now does an O(1) dictionary lookup to find the correct bucket instead of iterating all type buckets (was O(k×n))
• The side-map is maintained on add, remove, and removeAll

Closes #139

Test plan

• swift build succeeds
• All 1576 tests pass (swift test)