Fix the directory functionality of clan (clan.directory).
The python API interface was not able to distinguish if the directory
was set to anything other than `self.src`.
Breaking every command that relied on the clan directory, for example:
- `clan machines update`
- `clan machines update-hardware-config`
See more in #2906
This is the first step in fixing all those commands.
Individual command support and implementation will be implemented in
follow ups.
This now gives a clearer error than:
```
Traceback (most recent call last):
File "/nix/store/mznnb8il3njp6jxn5i57d0myjdh6cs0i-clan-cli/bin/.clan-wrapped", line 9, in <module>
sys.exit(main())
~~~~^^
File "/nix/store/mznnb8il3njp6jxn5i57d0myjdh6cs0i-clan-cli/lib/python3.13/site-packages/clan_cli/cli.py", line 516, in main
args.func(args)
~~~~~~~~~^^^^^^
File "/nix/store/mznnb8il3njp6jxn5i57d0myjdh6cs0i-clan-cli/lib/python3.13/site-packages/clan_cli/vars/check.py", line 113, in check_command
ok = check_vars(args.machine, args.flake, generator_name=args.generator)
File "/nix/store/mznnb8il3njp6jxn5i57d0myjdh6cs0i-clan-cli/lib/python3.13/site-packages/clan_cli/vars/check.py", line 103, in check_vars
status = vars_status(machine_name, flake, generator_name=generator_name)
File "/nix/store/mznnb8il3njp6jxn5i57d0myjdh6cs0i-clan-cli/lib/python3.13/site-packages/clan_cli/vars/check.py", line 41, in vars_status
generators = Generator.generators_from_flake(machine.name, machine.flake)
File "/nix/store/mznnb8il3njp6jxn5i57d0myjdh6cs0i-clan-cli/lib/python3.13/site-packages/clan_cli/vars/generate.py", line 67, in generators_from_flake
generators_data = flake.select_machine(
^^^^^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'select_machine'
```
When not being in a flake.
Motivation: updating a machine fails, if it depends on a private github repo, as the remote will likely not be authenticated.
This adds a new flag `--fetch-local` to `clan machines update` which fetches all flake inputs prior to building, then uploads them to the build-host.
This also adds a new error message, when flake inputs could not fetched, to hint the user to use `--fetch-local`
ignoring SLF001 (private member access) globally is not ideal, as it disables a valuable check throughout the entire codebase
disable SLF001 only for test files instead
Fix clan template creation when already in a flake.
Currently we already fail with very clear and descriptive error when
trying to evaluate the template of the flake we are in:
```
Failed to select template 'flake-parts' from flake '/tmp/superclan' (via attribute path: /tmp/superclan#clanInternals.templates.clan."flake-parts")
```
This is undesired behavior.
When we are trying to create a clan with `clan flakes create`.
We can't rely on the fact that the flake we are currently in exports flake templates.
Now we *try* to evaluate the flake we are in upon creation.
If there are no clan templates available, we now will fall back to
builtin templates.
Closes: #4472
