Implement Watcher Testing

[frrist]

Description

Test lily watcher package in isolation of its indexer. Test should assert that watcher passes expected tipsets to its indexer, they need not assert it writes the data to the database.

Acceptance criteria

• Watcher works with confidence of 1
• Watcher tolerates reorgs
• Watcher coverage for current, apply, and revert operations
• Watcher handles failure case when notifier fails unexpectedly

Where to begin

watcher_test.go