Implement interactive tx construction protocol via `InteractiveTxCons…

…tructor`

This implements the interactive construction protocol described at
https://github.com/lightning/bolts/blob/78e5a6b066d3a8e235931dfc06aa325337874749/02-peer-protocol.md?plain=1#L92.

Our implementation includes a state machine with typed states and transitions
to ensure consumers have compile-time assurances that the protocol is upheld.

States are tracked as in the `StateMachine` enum and can take on all
possible states during the negotiation.

The states are further divided into two categories, namely by the two traits
they implement, either `ReceivedMsgState` or `SentMsgState`.

The defined `StateTransitions` enforce the transitions that `ReceivedMsgState`,
`SentMsgState`, and the `_TxComplete`s can go through.

Co-authored-by: Wilmer Paulino <[email protected]>
Co-authored-by: Duncan Dean <[email protected]>
Co-authored-by: Jurvis Tan <[email protected]>

lightning/src/events/bump_transaction.rs

@@ -41,11 +41,11 @@ use bitcoin::secp256k1;
 use bitcoin::secp256k1::{PublicKey, Secp256k1};
 use bitcoin::secp256k1::ecdsa::Signature;
 
-const EMPTY_SCRIPT_SIG_WEIGHT: u64 = 1 /* empty script_sig */ * WITNESS_SCALE_FACTOR as u64;
+pub(crate) const EMPTY_SCRIPT_SIG_WEIGHT: u64 = 1 /* empty script_sig */ * WITNESS_SCALE_FACTOR as u64;
 
 const BASE_INPUT_SIZE: u64 = 32 /* txid */ + 4 /* vout */ + 4 /* sequence */;
 
-const BASE_INPUT_WEIGHT: u64 = BASE_INPUT_SIZE * WITNESS_SCALE_FACTOR as u64;
+pub(crate) const BASE_INPUT_WEIGHT: u64 = BASE_INPUT_SIZE * WITNESS_SCALE_FACTOR as u64;
 
 /// A descriptor used to sign for a commitment transaction's anchor output.
 #[derive(Clone, Debug, PartialEq, Eq)]