lint: isort pre-commit & misc improvements (#3749)

* test: clean flake8 config root clutter

* test: pre-commit: add isort

Compatible with black (see https://github.com/timothycrosley/isort/issues/694)

* lint: reorder imports

* lint: more complex imports

* lint: fix deepsource

* config: isort: add first party dvc

* tests: restyled: add isort

* temp commit to revert before merge

* Revert "temp commit to revert before merge"

This reverts commit 11db0fd8e95fe891597cbb9bf804480909b19e24.

tests/func/test_lockfile.py

@@ -4,14 +4,13 @@ from textwrap import dedent
 
 import pytest
 import yaml
+
 from dvc.dvcfile import PIPELINE_LOCK
 from dvc.serialize import get_params_deps
 from dvc.utils.fs import remove
 from dvc.utils.stage import parse_stage_for_update
-
 from tests.func.test_run_multistage import supported_params
 
-
 FS_STRUCTURE = {
     "foo": "bar\nfoobar",
     "bar": "foo\nfoobar",