Use ruff isort plugin instead of isort

[farmio]

• Use ruff isort plugin instead of isort
• Move ruff to separate tox env (so dependabot updates can trigger a run - which doesn't work for update pre-commit hoos script)
• Run ruff in pre-commit only on pre-commit
• Remove isort from requirements
• Remove black target_version as it is now inferred from project.requires-python

[codecov]

Codecov Report

Merging #321 (95d81f3) into main (fc57075) will increase coverage by 0.02%.
Report is 1 commits behind head on main.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #321      +/-   ##
==========================================
+ Coverage   97.48%   97.50%   +0.02%     
==========================================
  Files          21       21              
  Lines        1073     1082       +9     
==========================================
+ Hits         1046     1055       +9     
  Misses         27       27              

see 3 files with indirect coverage changes