chore: add a cyclomatic complexity plugin to pylint

This commit add a feature commented by @jaonoctus on a [\selfcustody#847
comment](https://github.com/selfcustody/krux/pull/847/changes#r3029819808),
where an review about multiple lines review could be avoided
automatically if we apply the `mccabe` plugin to `pylint`.

E.g, visually complexity could lead humans to interpret some lines as
complex given a experience of how code should be or not to be; some
standars could say that 25 lines could be the limit of a readability.
But a cyclomatic complexity on a function could be used as a "how real
complex is the function" and "it should be really refactored?".

Tested with `max-complexity=13` and `max-complexity=20` in tags
`v26.03.0`, branches `main`, `develop` and
`feat/stackbit-1248-vertical`. For more details about values a wikipedia
short ref:

* 1–10: Simple procedure: `little risk`;
* 11–20: More complex: `moderate risk`;
* 21–50: Complex: `high risk`.
* > 50: Untestable code: `very high risk`;

For now, this commit found 7 `too-complex` functions on source code
base.

Author: qlrd

pyproject.toml

@@ -84,7 +84,7 @@ black.ref = "format"
 format-test.ref = "format-tests"
 
 # pylint tasks
-lint-src = "pylint src"
+lint-src = "pylint --load-plugins=pylint.extensions.mccabe --max-complexity=20  src"
 lint-scripts = "pylint firmware/font/*.py firmware/scripts/*.py i18n/*.py"
 lint = ["lint-src", "lint-scripts"]
 # aliases
@@ -101,6 +101,7 @@ test-clean = """python -c 'import shutil, os; os.path.exists("htmlcov") and shut
 test-cov = "pytest --cache-clear --cov src/krux --cov-report html ./tests --cov-context=test --cov-report term-missing"
 test-verbose = "pytest --cache-clear --cov src/krux --cov-report html --show-capture all --capture tee-sys -r A ./tests"
 test-simple = "pytest --cache-clear ./tests"
+
 # aliases
 tests = ["test-clean", "test-cov"]
 test.ref = "tests"