Introduce flake8 complexity

• .flake8 configuration:

max-complexity = 8

• Reduce complexity of Silkaj code: long functions/methods, many arguments to a function/method prompt

changed milestone to %Backlog

added Dev Env enhancement labels

mentioned in issue #424 (closed)

marked this issue as related to #424 (closed)

removed milestone %Backlog

Will be done together with other Ruff rules in #460.

closed