refactor(yaml): move loader and dumper files

[timreichen]

• moves _loader/loader.ts to _loader.ts
• moves _dumper/dumper.ts to _dumper.ts

[codecov[bot]]

Codecov Report

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

Project coverage is 95.70%. Comparing base (735609e) to head (68ab333).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #5270 +/- ## ======================================= Coverage 95.70% 95.70% ======================================= Files 459 459 Lines 38025 38025 Branches 5563 5563 ======================================= Hits 36393 36393 Misses 1591 1591 Partials 41 41 ```

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