Improve performance of changelogger-validate-all.sh

[anomiex]

Proposed changes:

changelogger version is unnecessarily calling git to fetch the timestamp and PR number for all the changelog entries, when all it's really using is the significance. Skip that.

Then, while validating each individual project is reasonably fast, when there's 117 of them it adds up. We can improve things somewhat by processing projects in parallel, matching the number of processors in the system.

On my laptop, the first takes the time from ~16.8s to ~10.7s, and the second (8 cores) takes it to ~2.3s.

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

None

Does this pull request change what data or activity we track or use?

No

Testing instructions:

• Try it?

[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WordPress.com Simple site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin, and enable the fix/improve-performance-in-changelogger-validate-all branch.

  • For jetpack-mu-wpcom changes, also add define( 'JETPACK_MU_WPCOM_LOAD_VIA_BETA_PLUGIN', true ); to your wp-config.php file.

• To test on Simple, run the following command on your sandbox:

  bin/jetpack-downloader test jetpack fix/improve-performance-in-changelogger-validate-all
  

  bin/jetpack-downloader test jetpack-mu-wpcom-plugin fix/improve-performance-in-changelogger-validate-all
  

Interested in more tips and information?

• In your local development environment, use the jetpack rsync command to sync your changes to a WoA dev blog.
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• Figure out when your changes will be shipped to customers here: PCYsg-eg5-p2

[github-actions]

Thank you for your PR!

When contributing to Jetpack, we have a few suggestions that can help us test and review your patch:

• ✅ Include a description of your PR changes.
  
• ✅ Add a "[Status]" label (In Progress, Needs Team Review, ...).
  
• ✅ Add testing instructions.
  
• ✅ Specify whether this PR includes any changes to data or privacy.
  
• ✅ Add changelog entries to affected projects
  

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[zinigor]

Before:

$ time ./tools/changelogger-validate-all.sh

real	0m17,171s
user	0m9,760s
sys	0m6,802s

After:

$ time ./tools/changelogger-validate-all.sh

real	0m0,837s
user	0m8,717s
sys	0m6,285s

Very impressive!

[tbradsha]

Noting that nproc doesn't exist on macOS. It seems sysctl -n hw.physicalcpu is an equivalent:

memkind/memkind#33 (comment)

[tbradsha]

#38141