merged code coverage isn't accurate

[Yokozuna59]

Description

The merged code coverage of vitest and cypress isn't accurate; it's reporting wrong and alternating results. For example, in reports from codecov, if someone updated a file, even if it had no effect on actual code, the coverage percentage would differ. See this PR: #4541 (comment). It shows that the coverage has increased, but the only file that has changed is a github workflow file.

Steps to reproduce

Just merge the code coverage using scripts/coverage.ts script.

Screenshots

No response

Code Sample

No response

Setup

• Mermaid version: doesn't matter
• Browser and Version: doesn't matter

Suggested Solutions

The issue is from nyc side, there is an open issue for with some suggested solutions there: istanbuljs/nyc#1302

Additional Context

No response

[Yokozuna59]

@sidharthv96 I think we should reopen this issue, the current coverage is 45%:

https://app.codecov.io/github/mermaid-js/mermaid/commit/194ef202ac5df51056d98c14f13e9ca85f274c35