refactor(ts): refactor db module to use TS and ESM

[jescalada]

Fixes #964.

This PR refactors the db module to use TS and ESM. It builds on top of #929 (the latest commits haven't been merged in yet).

Original PR comment:

My biggest concern is the implications of CommonJS and ESM interoperation. Is it desirable to use ESM, or should we stick to CommonJS? I thought using ESM would make the project more future-proof and allow more modern syntax, but getting things to work has been a massive headache.

Specifically, it's a pain to get tests to work while mixing JS/TS and CommonJS/ESM.

Right now, I'm stuck with a problem with the plugin tests, which depend on an ESM-only module (load-plugin). I'm not sure if this is a compatibility bug or if there's an easy way to fix it on the git-proxy side, but I've tried a few workarounds without any luck.

If ESM is problematic, I can roll back the export changes while keeping the TS stuff in.

Edit: I've managed to get the tests to pass by using mocha on the plugin tests and ts-mocha on everything else. The only problem is that some recent tests are flaky on local (they seem to pass reliably in the CI):

Edit 2: Fixed flaky tests in #945.

Thank you!

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[codecov]

Codecov Report

Attention: Patch coverage is 59.16667% with 49 lines in your changes missing coverage. Please review.

Project coverage is 51.70%. Comparing base (83e814b) to head (478703b).

Files with missing lines	Patch %	Lines
src/db/file/pushes.ts	48.48%	17 Missing ⚠️
src/db/index.ts	42.85%	11 Missing and 5 partials ⚠️
src/db/file/repo.ts	60.52%	15 Missing ⚠️
src/db/file/users.ts	92.85%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #938       +/-   ##
===========================================
- Coverage   61.88%   51.70%   -10.18%     
===========================================
  Files          49       48        -1     
  Lines        1805     1671      -134     
  Branches        0       53       +53     
===========================================
- Hits         1117      864      -253     
- Misses        688      790      +102     
- Partials        0       17       +17     

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