For the final hop in a blinded route, the SCID and RelayInfo fields will
_not_ be set. So these fields need to be converted to optional records.
The existing BlindedRouteData constructor is also renamed to
`NewNonFinalBlindedRouteData` in preparation for a
`NewFinalBlindedRouteData` constructor which will be used to construct
the blinded data for the final hop which will contain a much smaller set
of data. The SCID and RelayInfo parameters of the constructor are left
as non-pointers in order to force the caller to set them in the case
that the constructor is called for non-final nodes. The other option
would be to create a single constructor where all parameters are
optional but I think this makes it easier for the caller to make a
mistake.
We may get a flake like the following,
```
lnd_route_blinding_test.go:468:
Error Trace: /Users/runner/work/lnd/lnd/itest/lnd_route_blinding_test.go:468
/Users/runner/hostedtoolcache/go/1.22.3/arm64/src/runtime/asm_arm64.s:1222
Error: Received unexpected error:
rpc error: code = Canceled desc = context canceled
Test: TestLightningNetworkDaemon/tranche15/144-of-156/bitcoind/disable_introduction_node
```
This happens when the test successfully finishes, the parent context is
canceled, causing the child context to return an error. We fix it by
ignoring it in the goroutine.
We mine quite a few blocks in this test to trigger a htlc timeout,
so it can be pretty slow. This fix adds assertions for additional
"state steps" that happen in between the failing of the htlc on-chain
and asserting that we're fully cleared out so that slower running
machines won't timeout.
This itest adds a test that we still propagate blinded errors back
properly after a restart with an on-chain resolution. The test also
updates our sendpayment timeout to longer so that there's time to
resolve the on chain claim.
We don't support receiving blinded in this PR - just intercept and
settle instead. The HTLC's arrival on the interceptor indicates that
it was successfully forwarded on a blinded hop.
