Test coverage improvements

[danielnaab]

This PR adds improvements to the test suite:

• a vitest workspace was added, to speed up running each project's tests at once
• a shared vitest config was added to the root. it turns out this is not useful for coverage settings in Vitest, which seem to need to be specified via command-line. However, this will be useful later, so I'm keeping it in.
• vitest-github-actions-reporter was added to the CI test run. This will add annotations to the diff view (click "Files changed" on the PR) for each test failure.
• A shared Github action, davelosert/[email protected], was added. This adds a comment to each PR with the test coverage.

Note, these improvements are only to the Vitest portion of the tests. There are also Jest tests in the CDK Terraform project (infra directory), which are not included. Nonetheless, they are still run as part of the CI.

[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	74.83%	2001 / 2674
🔵	Statements	74.83%	2001 / 2674
🔵	Functions	41.95%	60 / 143
🔵	Branches	77.39%	89 / 115

File Coverage

File	Stmts	% Branch	% Funcs	% Lines	Uncovered Lines
Changed Files
packages/documents/src/pdf/extract.ts	76.27%	80%	100%	76.27%	37-43, 45-51
packages/form-service/src/context/browser/form-repo.ts	47.66%	57.14%	44.44%	47.66%	8-9, 12-13, 18-27, 30-44, 54-58, 65-66, 72-74, 84-85, 91-97, 100-107

Generated in workflow #64