Re-export `lightning_types` in top-level `lightning` modules

[TheBlueMatt]

Since we now have many types in one place, it makes sense to export them in that place. Further, doing so finally somewhat starts to reduce our lightning::ln module size, which historically is the dumping ground for everything when most things really should be top-level modules in lightning.

Here we take a step in the right direction by exporting lightning_types as lightning::types and encouraging users to use those paths directly rather than the ones in lightning::ln.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 89.70%. Comparing base (ccce9d9) to head (1e1b8ec). Report is 34 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #3253 +/- ## ========================================== + Coverage 89.68% 89.70% +0.01% ========================================== Files 124 124 Lines 102386 102386 Branches 102386 102386 ========================================== + Hits 91827 91844 +17 + Misses 7857 7839 -18 - Partials 2702 2703 +1 ```

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