Add a `require_flake` function that checks, if no argument is passed, if
we are in a clan directory.
If not will throw a helpful error.
Before `clan show`:
```
Traceback (most recent call last):
File "/nix/store/8kb3l3yvz6svygnxdlrw5lmd3h3chc8a-clan-cli/bin/.clan-wrapped", line 9, in <module>
sys.exit(main())
~~~~^^
File "/nix/store/8kb3l3yvz6svygnxdlrw5lmd3h3chc8a-clan-cli/lib/python3.13/site-packages/clan_cli/cli.py", line 493, in main
args.func(args)
~~~~~~~~~^^^^^^
File "/nix/store/8kb3l3yvz6svygnxdlrw5lmd3h3chc8a-clan-cli/lib/python3.13/site-packages/clan_cli/clan/show.py", line 12, in show_command
meta = get_clan_details(flake)
File "/nix/store/8kb3l3yvz6svygnxdlrw5lmd3h3chc8a-clan-cli/lib/python3.13/site-packages/clan_lib/clan/get.py", line 22, in get_clan_details
if flake.is_local and not flake.path.exists():
^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'is_local'
```
with `require_flake`:
```
No clan flake found in the current directory or its parents - Use the --flake flag to specify a clan flake path or URL
```
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