Add LDK Node integration test

[tnull]

We add a simple workflow to our CI that runs cargo check on LDK Node to ensure LDK didn't introduce breaking API changes.

The idea here is to catch breaking changes early, and encourage to fix them in LDK or LDK Node main ASAP.

In the future we might want to extend this to run the full test suite, once we whack-a-moled a few more of LDK Node's flaky tests.

[ldk-reviews-bot]

👋 Thanks for assigning @joostjager as a reviewer!
I'll wait for their review and will help manage the review process.
Once they submit their review, I'll check if a second reviewer would be helpful.

[joostjager]

Simple and cool

[joostjager]

Use something like "LDK Node build compatibility check" for now? Can update the name once the integration tests are actually ran.

[tnull]

Hmm, I intentionally left it more general for now.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.30%. Comparing base (2d6e017) to head (f50ea31).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #4206 +/- ##
=======================================
Coverage 89.29% 89.30% =======================================
Files 180 180 Lines 137913 137913 Branches 137913 137913 =======================================
+ Hits 123144 123157 +13 + Misses 12154 12147 -7 + Partials 2615 2609 -6 

Flag	Coverage Δ
fuzzing	33.58% <ø> (+0.90%)	⬆️
tests	88.69% <ø> (+<0.01%)	⬆️

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[tnull]

Will just land this, as it's simple enough and we can make further changes.