Extends the SQL store to support v2 (taproot) channel announcements:
- Add version validation in AddChannelEdge
- Store v2-specific fields: FundingPkScript, MerkleRootHash, Signature
- Update buildEdgeInfoWithBatchData to reconstruct v2 channels from DB
with optional bitcoin keys and funding script handling
- Add WithMerkleRootHash edge modifier for ChannelV2Fields