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/unit/command/test_diff.py

@@ -1,6 +1,6 @@
 import collections
-import os
 import logging
+import os
 
 from dvc.cli import parse_args
 

tests/unit/command/test_metrics.py

@@ -1,5 +1,5 @@
 from dvc.cli import parse_args
-from dvc.command.metrics import CmdMetricsDiff, _show_diff, CmdMetricsShow
+from dvc.command.metrics import CmdMetricsDiff, CmdMetricsShow, _show_diff
 
 
 def test_metrics_diff(dvc, mocker):

tests/unit/command/test_plot.py

@@ -1,7 +1,7 @@
 import pytest
 
 from dvc.cli import parse_args
-from dvc.command.plot import CmdPlotShow, CmdPlotDiff
+from dvc.command.plot import CmdPlotDiff, CmdPlotShow
 
 
 def test_metrics_diff(mocker):

tests/unit/command/test_update.py

@@ -1,4 +1,5 @@
 import pytest
+
 from dvc.cli import parse_args
 from dvc.command.update import CmdUpdate