Always print JSON output with --format json

[charliermarsh]

Summary

Closes #3670.

Test Plan

uv on  charlie/list:main
❯ cargo run pip list --editable
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.15s
     Running `target/debug/uv pip list --editable`
uv on  charlie/list:main
❯ cargo run pip list --editable --format json
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.16s
     Running `target/debug/uv pip list --editable --format json`
[]
uv on  charlie/list:main
❯ cargo run pip list --editable --format freeze
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.15s
     Running `target/debug/uv pip list --editable --format freeze`
uv on  charlie/list:main
❯ cargo run pip list --editable --format columns
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.15s
     Running `target/debug/uv pip list --editable --format columns`