feat: support reproducible builds using SOURCE_DATE_EPOCH

[peterhirn]

🔗 Linked issue

#2645

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

If environment variable SOURCE_DATE_EPOCH is set (number seconds since the Unix epoch) use this timestamp instead of new Date() and mtime. See linked issue for more context.

Resolves #2645

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

TODO

• Documentation (is a change to the docs for this feature desired?)
• Preferred code formatting/style (please advice on how you would like this code to be formatted)
• Investigate if there are additional new Date() or mtime calls to patch
• Investigate if fixed mtime can introduce bugs at runtime
• e2e test (atm I only tested this using pnpm patch)
• merge to v3 (or would you prefer to create this pr against main, then backport?)