Add Solana finality logic: commitment level tracking #33
Description
Summary
Implement Solana finality strategy tracking commitment levels: processed (~400ms), confirmed (~5s), finalized (~6-12s).
Changes
- Poll transaction signature status with increasing commitment levels
- Map Solana commitment levels to finality states
- Emit confirming events at processed and confirmed
- Emit finalized when commitment = finalized
Tests
- Commitment progression triggers correct state transitions
- Finalized commitment maps to finalized state
Acceptance Criteria
Solana finality tracking reflects Tower BFT commitment levels.