[IMP] plugin: search, list and inspect odev plugins - #174

…e ones

#174 added a TestGithubConnectorRepositories class to this module, and both branches narrowed
its imports to what they needed. Both sets of classes are kept and the imports are the union of
the two.

Also bumps the version to 4.31.3, one increment above the base branch.

## Description

`odev plugin` could only enable, disable or show a plugin whose name you already knew. This PR adds discovery to the command, and makes `--show` the detail view for every plugin odev can know about.

- **`odev plugin --search [terms]`** — searches GitHub for published plugins, keeping only repositories exposing a valid manifest at their root. The `odev` keyword alone is unusable (it collides with unrelated repositories, mostly Turkish *ödev*), so repositories are matched on both `odev` and `plugin` in name, description or topics; on the current index that returns 13 real plugins out of 14 hits. Archived repositories and [the template repository](https://github.com/odoo-odev/odev-plugin-template), which cannot be installed, are left out. `--limit` caps how many repositories are inspected (20 by default), bounding the cost to `1 + N` API requests.
- **`odev plugin --list`** — every plugin available locally with its state: `enabled`, `disabled` (downloaded but not linked), `missing` (link gone) or `shadowed`. That last state was previously invisible: two enabled plugins forked from one another map to the same module name and only one is ever loaded — which is the case today for `odoo-odev/odev-plugin-editor-vscode` and its `avanserv` fork.
- **`odev plugin --show`** — now built on the same discovery, so it reports states consistently with `--list`. A plugin that is not on the machine is looked up on GitHub, so uninstalled and never-downloaded plugins are described too; plugins present locally are read from disk and never trigger a request. Failing to reach GitHub falls back to the local information instead of raising. Without an argument, `--show` details every local plugin rather than the enabled ones only.

Searching and listing never install anything — installing remains `odev plugin --enable <organization>/<repository>`.

Supporting changes:

- **`parse_plugin_manifest()`** (`odev/common/odev.py`) — reads a manifest with `ast`, taking only the module docstring and top-level literal assignments. Manifests are otherwise loaded through `exec_module`, which is fine for a repository the user explicitly installed but unacceptable for arbitrary search results. A top-level `__version__` string is what identifies a repository as an odev plugin. `plugin_module_name()` is extracted at the same time, replacing the same expression repeated in four places.
- **`GithubConnector`** (`odev/common/connectors/git.py`) — `GitConnector` requires an `organization/repository` at construction, so there was nowhere for a search to live. The API connection concern is extracted into a new base class (a pure move of the token, connection and authentication members; `GitConnector` inherits from it and keeps its public API), which gains `search_repositories()`, `get_repository()` and `get_repository_file()`. All three return `None` rather than raising when a result is missing or unreadable.

Also fixes `--show <organization>/<repository>`, which **always** reported a plugin as disabled: the name was stripped of its organization before being compared to the enabled plugins, which are stored fully qualified. A repository name on its own is now accepted too, as long as it is not ambiguous.

## Testing

- Full test suite: **165 passed** (143 → 157 → 165; 18 new tests covering the manifest parser, the connector and the three command modes), py3.14, local PostgreSQL.
- `pre-commit run --all-files` clean; `basedpyright` reports no new error against the baseline.
- Exercised against the real GitHub API from a live checkout: `--search`, `--search ai`, `--search` with no result, `--list`, and `--show` on an enabled plugin (no request), the template repository (template warning, no install hint), an archived plugin (archived warning), a non-existent repository, the shadowed `avanserv` fork, a bare unknown name, and with no argument.
- A manifest containing `os.system(...)` and `raise SystemExit(1)` at module level is parsed with no side effect (covered by a unit test).

## Compliance

- [x] I have read the [contribution guide](../docs/CONTRIBUTING.md)
- [x] I made sure the documentation is up-to-date both in doctrings and the `docs` directory
- [x] I have added or modified unit tests where necessary
- [x] I have added new libraries to the `requirements.txt` file, if any
- [x] I have incremented the version number according the [versioning guide](../../docs/contributing/versioning.md)
- [x] The PR contains **my changes only** and **no other external commit**

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