chore: replace `execa` with `tinyexec`

[pralkarz]

This PR replaces execa with a lighter alternative.

Some notes:

1. tinyexec only provides an asynchronous API. My changes aim to keep the existing behavior through async/await, while also following the ESLint rules (e.g. not inlining (await func(...)).stdout but extracting the await output to a separate variable).
2. I went ahead and added some miscellaneous things to .gitignore for smoother DX. 😄
3. I tackled the comments regarding mocking execaSync (now x). Please let me know if you'd prefer to keep the old approach.

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🦋 Changeset detected

Latest commit: 00d1b94a3bbb99a39b323a79db246cc728da6abe

The changes in this PR will be included in the next version bump.

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pretty-quick	Minor

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[JounQin]

Sorry I didn't notice this PR for a long time, seems great.