Merge pull request #3125 from valentinewallace/2024-06-async-payments-prefactor

Async payments message encoding and prefactor

diff --cc lightning/src/ln/channelmanager.rs
Simple merge

diff --cc lightning/src/ln/functional_test_utils.rs
Simple merge

diff --cc lightning/src/ln/offers_tests.rs
Simple merge

diff --cc lightning/src/onion_message/functional_tests.rs
Simple merge

diff --cc lightning/src/onion_message/messenger.rs
Simple merge