v1: Move snapshot threshold and trailing configs to legacy layer

[codecov[bot]]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (1e6406f) 74.15% compared to head (754530f) 74.15%.

Files	Patch %	Lines
src/legacy.c	83.33%	0 Missing and 2 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #173 +/- ## ========================================== - Coverage 74.15% 74.15% -0.01% ========================================== Files 52 52 Lines 10369 10360 -9 Branches 2467 2466 -1 ========================================== - Hits 7689 7682 -7 + Misses 1324 1323 -1 + Partials 1356 1355 -1 ```

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