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/view.md

@@ -0,0 +1,18 @@
+# View a Pull Request
+
+> `n34 pr view` command
+
+**Usage:**
+```
+Usage: n34 pr view [OPTIONS] <EVENT-ID>
+
+Arguments:
+  <EVENT-ID>  Pull request ID
+
+Options:
+      --repo <NADDR-NIP05-OR-SET>  Repository addresses
+```
+
+View a specific pull request. This includes the pull request title, labels,
+description, clone URLs, and the latest commit tip. Use this information to
+fetch the changes.