Bump btcec to v2, use integrated btcutil module

[guggero]

Extracted out from #6263.

This PR switches lnd over to using the new btcec/v2 and btcutil modules located in the btcsuite/btcd repo.

All commits starting with SQUASHME will be squashed into a single commit before merging. They are only pushed separately for easier review.

[Roasbeef]

Seeing this test failure uniformly:

--- FAIL: TestLightningWallet (114.32s)
    --- FAIL: TestLightningWallet/btcwallet/neutrino:publish_transaction (15.92s)
        test_interface.go:1914: expected ErrDoubleSpend, got: <nil>

I think it might be due to: lightninglabs/neutrino#240 ?

[Roasbeef]

I think you may need to go into each sub-module and to go mod tidy, so it can pick up other dependencies like the psbt package.

[guggero]

I think it might be due to: lightninglabs/neutrino#240 ?

Yes, you were right. It looks like that PR didn't account for reject messages correctly. I created a fix for it in lightninglabs/neutrino#247 and downgraded this PR to a version just before lightninglabs/neutrino#240 was merged.

[lightninglabs-deploy]

@guggero, remember to re-request review from reviewers when ready

[Roasbeef]

Needs a rebase! We'll eventually update to that neutrino version before we tag the next major release, so fine w/ going with the downgraded version here.

[guggero]

Rebased.

[guggero]

Rebased again. @positiveblue PTAL.

[Roasbeef]

Modules pops up with this warning:

no required module provides package github.com/btcsuite/btcd/btcutil/gcs/builder; to add it:

I think it's missing a go mod tidy somewhere? But perhaps it's also just due to the set of intermediate commits.

[Roasbeef]

LGTM 🍭

Now that the PR uses the prior version of neutrino, we're no longer blocked on that fix, allowing us to move forward here on the taproot front!

[guggero]

Modules pops up with this warning:

no required module provides package github.com/btcsuite/btcd/btcutil/gcs/builder; to add it:

I think it's missing a go mod tidy somewhere? But perhaps it's also just due to the set of intermediate commits.

Yeah, the intermediate commits (prefixed with SQUASHME-) won't build on their own. My plan is to squash them into a single commit before merging.

[positiveblue]

LGTM @guggero thanks for splinting this in its own PR

The errors that Github actions show are only because some of the commits do not compile by itself but after squashing everything should pass (as it does in the last commit)

[guggero]

Thank you for the review, @positiveblue!

Going to squash the commits prefixed with SQUASHME- into a single one.
Adding this comment here to preserve the split on GitHub:

Parts:

• 2d746f68: replace imports
• 4008f0fd: use ecdsa.Signature
• 849e33d1: remove btcec.S256()
• b8f6ebbd: use v2 library correctly
• fa80bca9: bump go modules