feat: support pull requests

Support for pull requests, it's not standard in NIPs yet[1] but there must be
two clients that support it to be included in NIPs, n34 is one of them.

This support:
- Create a new PR `n34 pr new`
- Update PR tip `n34 pr update`
- View a PR `n34 pr view`
- List PRs `n34 pr list`
- Add `PR` and `PR-update` kinds as roots in `NostrClient::find_root`
- Support issuing statuses for PRs
- Support GRASP PR and PR-update
- Update the docs

[1] https://github.com/nostr-protocol/nips/pull/1966

docs/pr/README.md

@@ -0,0 +1,43 @@
+# Pull Request Management
+
+Pull requests are a new addition to [NIP-34], proposed by [DanConwayDev] in
+[nostr-protocol/nips#1966]. The concept is straightforward: it involves an event
+that notifies you of changes on a Git server, which can be any Git server. This
+event contains two key pieces of information, the Git repository URL and the
+commit tip. You can add this remote to your project, check out the specified
+commit, and then review or merge/rebase the changes as needed. Additionally,
+there is a `PR-update` event that informs you when the previous commit tip is no
+longer the head of the changes, such as when new changes are added or a rebase
+occurs.
+
+## Why Use the Commit Tip?
+
+Using the commit tip is preferable to relying on a branch name. A branch name
+simply points to a commit, so checking out a branch is effectively the same
+as checking out a specific commit. However, if we use the branch name instead
+of the commit, the changes can be altered by anyone, not just the pull request
+author. By checking out a specific commit ID, we ensure that the changes are
+exactly as intended by the pull request author and have not been tampered with
+by a malicious party.
+
+## Does `n34` Handle Git Operations?
+
+No, `n34` does not perform any Git operations. You can use the `n34 pr view`
+command to retrieve the pull request clone URL and the commit tip, allowing
+you to fetch the changes manually. Similarly, `n34 pr new` and `n34 pr update`
+do not interact with Git directly. They only prompt you for the clone URL and
+commit tip to construct the event. For more details on the philosophy behind
+`n34`, refer to the [Philosophy] section.
+
+## Why use pull requests instead of patches?
+
+Pull requests are useful for large changes. Most relays limit events to 60KB,
+so if your changes exceed that limit (per event, not in total), consider using
+pull requests. For [GRASP] servers, the limit is usually higher. Before using pull
+requests, check the relays, patches are more decentralized.
+
+[NIP-34]: https://github.com/nostr-protocol/nips/blob/master/34.md
+[DanConwayDev]: https://danconwaydev.com
+[nostr-protocol/nips#1966]: https://github.com/nostr-protocol/nips/pull/1966
+[Philosophy]: https://n34.dev/commands.html#philosophy
+[GRASP]: https://ngit.dev/grasp