[feature]: Add lnd mock to mimick asset channel actions in order to improve testing

[dstadulis]

Is your feature request related to a problem? Please describe.

Given the Skip checks demonstrated in #1192, in situ RFQ testing requires exceptions for integration tests due to an inability to properly set up asset channels within exclusively the tapd code base. Ergo, flags like SkipAssetChannelCheck are a temporarily solution but they relax the validation certainty.

Describe the solution you'd like

Introduce a lnd-mock that will mimic asset channels, allowing tapd to test in a more accurate way without depending on validation-exemption flags.

Testing improvements, Easier test-code creation

The proposed mock could be used to test other features of tapd that currently rely on real lnd instances.

Describe alternatives you've considered

Continue using the validation-exemption flags testing setup s.a. SkipAssetChannelCheck flag, but this approach has limitations as we can't fully test the asset channel validation logic.

Related issues

• [rfq]: add validation to AddAssetBuyOrder and AddAssetSellOrder RPCs #1192 - [rfq]: add validation to AddAssetBuyOrder and AddAssetSellOrder RPCs
• Related discussion in PR comments: [rfq]: add validation to AddAssetBuyOrder and AddAssetSellOrder RPCs #1192