Redact registry credentials in lockfile (#5803)
## Summary
Okay, I tested this against...
- Our public "private" proxy
- Fury
- AWS CodeArtifact
- Azure Artifacts
It took a long time.
All of them work as expected with this approach: we omit the credentials
from the lockfile, then wire them back up when the index URL is provided
during subsequent operations.
Closes https://github.com/astral-sh/uv/issues/5119.
