## Summary
When we read `--index-url` from a `requirements.txt`, we attempt to
respect the `--index-url` provided by the CLI if it exists.
Unfortunately, `--index-url` from the CLI has a default value... so we
_never_ respect the `--index-url` in the requirements file.
This PR modifies the CLI to use `None`, and moves the default into logic
in the `IndexLocations `struct.
Closes https://github.com/astral-sh/uv/issues/1692.
First, replace all usages in files in-place. I used my editor for this.
If someone wants to add a one-liner that'd be fun.
Then, update directory and file names:
```
# Run twice for nested directories
find . -type d -print0 | xargs -0 rename s/puffin/uv/g
find . -type d -print0 | xargs -0 rename s/puffin/uv/g
# Update files
find . -type f -print0 | xargs -0 rename s/puffin/uv/g
```
Then add all the files again
```
# Add all the files again
git add crates
git add python/uv
# This one needs a force-add
git add -f crates/uv-trampoline
```
