docs: Add usage information and coverage report to docs

[kevintyj]

What is the purpose of this PR?

Add usage information and coverage report to docs. This will help users better utilize the action.

ClickUp/Jira/Github project ticket number(s)?

What did you do?

Add Vitest coverage report to CI pipeline
Reach 100% coverage
Add codecov to CI & repository
Fix ignore patterns for test reports

How do we test it?

Vitest test suites all passing

Checklist before merging

• Added tests where necessary
• Performed a self-review of my code
• Ensure all acceptance criteria are met
• Implemented the UI as exactly as the design (applicable only for UI changes)
• Added comments for codes where hard-to-understand
• Haven't pushed unnecessary files (ex: .env, .map)
• Haven't ignored Typescript warnings in the code (if do so add a comment with the reason)

Provide screenshot details of the PR

[optional] Tests passed screenshot

[optional] Breaking changes after PR

Anything else?

[codecov]

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