refactor(coverage): move re-usable parts to base provider

[AriPerkkio]

Description

• Refactors v8 and istanbul coverage providers by moving re-usable logic into base provider
• Note that we cannot move parts where dependencies of coverage providers are used as we don't want to bring those into vitest package

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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[AriPerkkio]

/ecosystem-ci run

[vitest-ecosystem-ci]

📝 Ran ecosystem CI: Open

suite	result
aria-live-capture	✅ success
nuxt	❌ failure
nuxt-test-utils	✅ success
elk	✅ success
effect	✅ success
zustand	✅ success
vue	✅ success
vite	✅ success
vitest-vscode	❌ failure
vitest-sonar-reporter	✅ success
vitest-github-actions-reporter	✅ success
vitest-browser-simple	✅ success
vitest-browser-examples	✅ success
vitest-coverage-large	✅ success
vitest-reporters-large	✅ success
vitest-benchmark-large	✅ success

[hi-ogawa]

-300 LOC 🎉