Add CLI startup speed benchmark

[bluwy]

Changes

• Support pnpm astro-benchmark cli-startup in root
• Support !bench cli-startup in PR comments (once merged)

Example output:

Making project: render-default
Finished making project: render-default
Benchmarking `astro --help`...
Done
Benchmarking `astro info`...
Done
Result preview:
==========
#### CLI Startup


| Command      | Avg (ms) | Stdev (ms) | Max (ms) |
| :----------- | -------: | ---------: | -------: |
| astro --help |   434.98 |      21.17 |   492.63 |
| astro info   |   468.74 |      28.54 |   527.03 |
==========

Testing

Ran pnpm astro-benchmark cli-startup locally. I did not test if the !bench PR comment would work, but it should following the other patterns.

Docs

n/a. The !bench command should be documented in CONTRIBUTING in general.

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Latest commit: 0eecda8

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[bluwy]

Forgot to put a note. This was needed because running node /path/to/astro.js directly yields no package manager, so adding the ?. to prevent an error while running the benchmark.

[ematipico]

We could fix it by adding a "Could not determine." label, I'll send a PR