Provide structured JSON output for pip index versions

[KrishanBhasin]

The first part of #13188, providing a structured JSON-formatted output for pip index versions command.

Usage:

❯ pip index versions build --json
{"name": "build", "versions": ["1.2.2.post1", "1.2.2", "1.2.1", "1.1.1", "1.0.3", "1.0.0", "0.10.0", "0.9.0", "0.8.0", "0.7.0", "0.6.0.post1", "0.5.1", "0.5.0", "0.4.0", "0.3.1.post1", "0.3.1", "0.3.0", "0.2.1", "0.2.0", "0.1.0", "0.0.4", "0.0.3.1", "0.0.2", "0.0.1"], "latest": "1.2.2.post1", "installed_version": "1.2.2.post1"}

which is properly formatted JSON - it prettifies to:

{
  "name": "build",
  "versions": [
    "1.2.2.post1",
    "1.2.2",
    "1.2.1",
    "1.1.1",
    "1.0.3",
    "1.0.0",
    "0.10.0",
    "0.9.0",
    "0.8.0",
    "0.7.0",
    "0.6.0.post1",
    "0.5.1",
    "0.5.0",
    "0.4.0",
    "0.3.1.post1",
    "0.3.1",
    "0.3.0",
    "0.2.1",
    "0.2.0",
    "0.1.0",
    "0.0.4",
    "0.0.3.1",
    "0.0.2",
    "0.0.1"
  ],
  "latest": "1.2.2.post1",
  "installed_version": "1.2.2.post1"
}

[krishanbhasin-px]

hey there, just wanted to gently ask if there's anything else this PR needs in order to proceed, alongside the related #13219?

[notatallshaw]

hey there, just wanted to gently ask if there's anything else this PR needs in order to proceed, alongside the related #13219?

I don't think there's anything waiting on you (it looks like you've addressed or responded to all review comments), a pip maintainer needs to take the time and responsibility to review, approve, and merge the PR.

I believe we are all volunteers doing this in our free time, and the cost to making mistakes in pip is somewhat high. Which can unfortunately leave PRs in a waiting state for longer than ideal.

I've already added both PRs to the 25.1 milestone so they're not forgotten. I've not reviewed this PR, but if we get close to 25.1 and it's still in need for a reviewer I will take a look.

[krishanbhasin-px]

No worries! I just wanted to check I hadn't missed something - I didn't mean to be putting pressure on anyone.

Thank you for adding the tags, and no rush from my side for anything on this.

[pfmoore]

Thanks for the reminder! This looks fine to me, you've addressed the points I raised so I'm happy to just merge this.

Thank you for the contribution 🙂