Fix vanilla channel interoperability with stock LDK

[bitwalt]

Fixes #148.

This PR validates and integrates plain-channel interoperability with stock LDK. The corresponding Rust-Lightning fix is RGB-Tools/rust-lightning#36.

Changes

• point the Rust-Lightning submodule at the reviewed interoperability branch until Integrate Tor Connection Options #36 lands
• update the expected plain-channel commitment fee from 9920 to 9060 sat, removing the 172 weight units reserved for an RGB OP_RETURN
• add a standalone stock ldk-node test fixture under src/test/interoperability/ldk-node
• run the ignored interoperability tests in a dedicated CI job

The fixture is a separate Cargo crate so this repository's [patch.crates-io] entries cannot replace its stock LDK dependencies. Its revision is locked for reproducible CI builds.

Coverage

Four tests cover:

• stock LDK opening a private channel, paying in both directions, and closing cooperatively
• stock LDK opening an announced channel that remains public, ready, and usable
• RLN opening a private channel, paying in both directions, and closing cooperatively
• an RGB channel offered to stock LDK never becoming ready

The successful private-channel payments also exercise invoice route hints without adding a separate route-hint assertion to this PR.

Merge order

RGB-Tools/rust-lightning#36 should merge first. Then this PR can restore the submodule URL to RGB-Tools and pin the merged commit before merging.

Validation

• cargo fmt --package rgb-lightning-node -- --check
• cargo fmt --manifest-path src/test/interoperability/ldk-node/Cargo.toml -- --check
• cargo check --all-targets
• cargo test interoperability --no-run
• git diff --check

Compatibility

The underlying Rust-Lightning fix changes wire and commitment transaction encoding. A release carrying it needs a coordinated upgrade for deployed channels. Persisted channel state itself is unchanged.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.74%. Comparing base (aa11b7c) to head (b0af20e).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #149      +/-   ##
==========================================
+ Coverage   87.69%   87.74%   +0.04%     
==========================================
  Files          16       16              
  Lines        8414     8459      +45     
==========================================
+ Hits         7379     7422      +43     
- Misses       1035     1037       +2     

Flag	Coverage Δ
rust	87.74% <ø> (+0.04%)	⬆️

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