Support `uv sync [--dry-run] --format=json`

[InSyncWithFoo]

(Opened as per the suggestion here. Part of #411 and #3199.)

Currently, uv sync --dry-run --script foo.py would output something like this:

Would create script environment at: [...]/uv/cache/environments-v2/foo-[...]

I'm interested in the path itself. Extracting it from the plain text output is rather inconvenient, however. A --format=json option could help with this.

An example output might look like:

{
    "environment": "[...]/uv/cache/environments-v2/foo-[...]",
    "executable": "[...]/uv/cache/environments-v2/foo-[...]/bin/python",
    "exist": false
}

This format, obviously, needs some design.

[x0rw]

The issue is that there is this 'logger', i don't know if i should disable it while formatting or format it's output as well, the later is quite hard to do

[x0rw]

@zanieb assign?

[zanieb]

I wouldn't worry about formatting the logger. That'll require a larger restructuring to use jsonlines output. Is the logger writing to stdout or stderr? If the latter, nothing needs to change there.

[iwinux]

IMO everything that might download things from the Internet might need a --dry-run flag. Sometimes I type a wrong package name to uv add and several hundreds MBs of unknown packages get downloaded and difficult to clean up.

[InSyncWithFoo]

This seems to have been resolved by #13689.