Improve performance of tests

[anton-trunov]

See the sub-issues:

[novusnota]

1. We can swap out the default Jest runner ts-jest with Rust one: https://swc.rs/docs/usage/jest
2. Make use of --shard and --maxWorkers options in GitHub Actions and in CLI setting. See this Reddit page & article.

If the above won't add much, we could migrate from Jest to Vitest, which has a compatible API, but is much lighter by design.

[Gusarich]

this was partially fixed (only for maps, but it's the longest test) in #941