refactor(coverage): move common parts to vitest package

[AriPerkkio]

Description

Now that coverages packages don't have to maintain compatibility with previous vitest versions in same major (#5208), we can move more reusable code into vitest package. This is only refactoring to reduce duplication.

Please don't delete this checklist! Before submitting the PR, please make sure you do the following:

• It's really useful if your PR references an issue where it is discussed ahead of time. If the feature is substantial or introduces breaking changes without a discussion, PR might be closed.
• Ideally, include a test that fails without this PR but passes with it.
• Please, don't make changes to pnpm-lock.yaml unless you introduce a new test example.

Tests

• Run the tests with pnpm test:ci.

Documentation

• If you introduce new functionality, document it. You can run documentation with pnpm run docs command.

Changesets

• Changes in changelog are generated from PR name. Please, make sure that it explains your changes in an understandable manner. Please, prefix changeset messages with feat:, fix:, perf:, docs:, or chore:.

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[hi-ogawa]

Looks good!

Just to confirm, is it intentional to not move magicast's parseModule to BaseCoverageProvider.updateThresholds? If we move it, then magicast dependency also has to go to main vitest package, so maybe that's a slight concern.

[AriPerkkio]

Just to confirm, is it intentional to not move magicast's parseModule to BaseCoverageProvider.updateThresholds?

Yes exactly - we want to avoid having it as dependency on vitest package: #4442 (comment).
It cannot even be a devDependency for types: #4442 (comment).

[hi-ogawa]

Thanks for the links. Good to know it was already discussed before 👍

[AriPerkkio]

Now that breaking changes inside same major version are fine this kind of issues can come up #5310 🤷‍♂️