perf(v2): skip runtime fileHash cache in prod & get timestamp asynchronously

[endiliey]

Motivation

• Skip fileHash caching on production calculation to improve build performance. The runtime cache is only useful in development.
• Obtain git timestamp for showLastUpdateAuthor/ showLastUpdateTime asynchronously instead of synchronously.

Not sure why we did it synchronously previously, but since we are using child_process under the hood to actually do the git call, its better in async

P.S: We also use execa instead of cross-spawn because https://github.com/sindresorhus/execa has more stars (2.7k vs 600). It also strips the final newline from the output so you don't have to do stdout.trim(), Cleans up spawned processes when the parent process dies and have more descriptive errors.

Have you read the Contributing Guidelines on pull requests?

yes

Test Plan

With fixtures of 1,026 docs and several runs

Before -~89s.

After ~~46s

The git call is indeed expensive, disabling showUpdatedAuthor and showUpdatedTime reduce first cold 'Load' time to only 4s. But well, this is still an optimization

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[docusaurus-bot]

Deploy preview for docusaurus-preview ready!

Built with commit 57f49ff

https://deploy-preview-1951--docusaurus-preview.netlify.com