pkgs/cli: Move the test folder inside the python module

Move the `tests` folder to `clan_cli/tests`.

As we now want part of our tests to live next to the functions that are
tested - tests that are not in the `/tests` module also need access to
the configured test fixtures that are exposed by the `pytest_plugins`
declaration.

The following folder structure doesn't support this model:

```
├── clan_cli
│   ├── api
│   │    └── api_init_test.py
├── tests/
│   ├── conftest.py
│   └── ...
```

Here `api_init_test.py` even when importing the test functions will not
have the fixtures configured.

There is a way to configure python to import the fixtures from another
[`project/module`](https://docs.pytest.org/en/stable/how-to/fixtures.html#using-fixtures-from-other-projects), but this seems to *generally* be discouraged.

So moving the `conftest.py` to the toplevel and the `/tests` folder into
the toplevel seems to be a sensible choice choice.

pkgs/clan-cli/clan_cli/tests/helpers/cli.py

@@ -0,0 +1,19 @@
+import argparse
+import logging
+import shlex
+
+from clan_cli import create_parser
+from clan_cli.custom_logger import print_trace
+
+log = logging.getLogger(__name__)
+
+
+def run(args: list[str]) -> argparse.Namespace:
+    parser = create_parser(prog="clan")
+    parsed = parser.parse_args(args)
+    cmd = shlex.join(["clan", *args])
+
+    print_trace(f"$ {cmd}", log, "localhost")
+    if hasattr(parsed, "func"):
+        parsed.func(parsed)
+    return parsed

pkgs/clan-cli/clan_cli/tests/helpers/nixos_config.py

@@ -0,0 +1,11 @@
+from collections import defaultdict
+from collections.abc import Callable
+from typing import Any
+
+
+def def_value() -> defaultdict:
+    return defaultdict(def_value)
+
+
+# allows defining nested dictionary in a single line
+nested_dict: Callable[[], dict[str, Any]] = lambda: defaultdict(def_value)

pkgs/clan-cli/clan_cli/tests/helpers/validator.py

@@ -0,0 +1,21 @@
+import subprocess
+
+
+class Error(Exception):
+    pass
+
+
+def is_valid_age_key(secret_key: str) -> bool:
+    # Run the age-keygen command with the -y flag to check the key format
+    result = subprocess.run(
+        ["age-keygen", "-y"],
+        input=secret_key,
+        capture_output=True,
+        text=True,
+        check=False,
+    )
+
+    if result.returncode == 0:
+        return True
+    msg = f"Invalid age key: {secret_key}"
+    raise Error(msg)