Run a periodic crash-test

[jonasfj]

• Rewrote crash_test.dart so that:
  • It runs markdown in an isolate, insuring that infinite-loops are handled.
  • Find all markdown files using a list of file extensions.
• Setup a periodic Github Action to run crash_test.dart weekly.

The crash_test.dart concept is a bit dumb, but it has found bugs a few times. This will download latest version of packages on pub.dev, on my desktop that takes about 25 minutes. I'm guessing that on Github Actions it'll run a bit slower :see_no_evil:

We could run it for all package versions, but there is like 10x more package versions than packages. It's more likely that we should run it for most packages or something else.

Or perhaps we can find a nice large corpus of markdown files somewhere else to use for crash-testing.

[coveralls]

Pull Request Test Coverage Report for Build 8174367064

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
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• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.002%) to 96.137%

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Totals
Change from base Build 7977582785:	0.002%
Covered Lines:	1543
Relevant Lines:	1605

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💛 - Coveralls