Testing FFI from C side

[myrrc]

Add Catch2 target and first tests for C API

[codspeed-hq]

Merging this PR will not alter performance

✅ 1016 untouched benchmarks
⏩ 1522 skipped benchmarks¹

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_{Comparing myrrc/ffi-testing (f807e70) with develop (8fd83ab)}

Footnotes

1. 1522 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[0ax1]

lgtm after the last comments are addressed