Splicing / Dual Funding

[jkczyz]

Splicing launched as beta in LDK 0.2 and LDK Node 0.7. Full splicing support involves completing the tasks below. This follows on the work detailed in #1621.

• RBF support
  • initiating
  • accepting
  • Cap number of RBFs (commitment_signed batch only allows for 20 anyway) Introduce FundingScope abstraction to ChannelMonitor #3663 (comment)
  • Filter out contributed inputs that also exist in previous negotiated-but-not-yet-locked splice attempts (dd2e394#r2370654851)
• On-chain monitoring
  • Closed channel balance API Refactor ChannelContext value fields into FundingScope #3592 (comment)
    • Emit DiscardFunding events for double spent splice transactions #4030
• Async signing
• Cancel prior to ChannelManager::funding_transaction_signed API
• 0-conf
  • Track past funding scopes until mature
• Opportunistic contributions (i.e., when counterparty initiates the splice)
• Mixed mode (i.e., both splice-in and splice-out)
• Sweep repo for TODO(splicing) and TODO(dual_funding)
• Integrate dual-funding