Adds a set of test cases that exercise the spontaneous AMP payment flow
with valid and invalid reconstructions, as well as with single and
multiple HTLCs. This also asserts that spontaneous AMP is gated behind
the existing AcceptKeysend flag.
In this commit, we add a String() method to the failure resolution
outcome. Without this, logs aren't very useful as the integer version of
the outcome is printed rather than the description.
This commit adds LinkErrors with failure details to htlcs which fail on
our incoming link. This change is made with the intention of notifying
detailed htlc failure reasons in sendHTLCError. The FailureDetail
interface is implemented on FailureResolutionResults so that they can
directly be used to enrich LinkErrors. sendHtlcError is updated to
take a LinkError in preparation for the addition of a htlcnotifier
which will notify the detail of the error.
This commit splits the resolution result enum into results divided
by outcome (settled, failed or accepted). This allows us to more
strictly control which resolution results can be used with which
HtlcResolution structs, to prevent the combination of a settle
resolution result with a failure resolution result, for example.
