Updating the mocks to be complete implementation of the underlying
interfaces is not always possible due to cross dependency issues.
This commit embeds the interfaces into the mocks so we can at least
always compile them.
This commit bumps LND and lndclient to make it possible to upgrade
taproot HTLC construction with a MuSig2 version. This is required to
support both old (MuSig2 0.4) and new (MuSig2 1.0) clients.