Update pre-commit config to use poetry environment

Add precommit hook for checking for merge conflicts
Add dev dep for blacken-docs
Add dev dep for pre-commit-hooks
Update all precommit hooks to use system language
Update toxfile to use new dev deps
Fix tox vs. precommit conflicts with reorder-python-imports

tox.ini

@@ -19,23 +19,14 @@ platform = linux
 ignore_errors = true
 require_locked_deps = true
 locked_deps =
+    pre-commit
+    pre-commit-hooks
+    black
+    blacken-docs
+    reorder-python-imports
     pylint
     mypy
-    black
-    reorder-python-imports
-    pre-commit
-allowlist_externals =
-    bash
 commands =
-    black {toxinidir}/tox_poetry_installer/
-    # Oh man this is a doozy. If submodules are ever added to this plugin this will break, but I'm
-    # frustrated enough at this point that I'll need to take another look at it later to fix that.
-    # reorder-python-imports doesn't support handling directories on the CLI
-    # (https://github.com/asottile/reorder_python_imports/pull/76) and because the command is
-    # invoked directly (see comment below) we need file globbing to work around it.
-    # The "--unclassifiable-application-module" is a work around for reorder-python-imports not
-    # properly detecting the top-level module when run in a bash-wrapped command like this.
-    bash -c "reorder-python-imports {toxinidir}/tox_poetry_installer/*.py --unclassifiable-application-module tox_poetry_installer"
     pre-commit run --all-files
     pylint --rcfile {toxinidir}/.pylintrc {toxinidir}/tox_poetry_installer/
     mypy --ignore-missing-imports --no-strict-optional {toxinidir}/tox_poetry_installer/
@@ -49,19 +40,9 @@ require_locked_deps = true
 locked_deps =
     pylint
     mypy
-    black
-    reorder-python-imports
-allowlist_externals =
-    bash
 commands =
-    black {toxinidir}/tests/
-    # These bash-wrapped commands hurt my face, but these tools expect directories to be valid
-    # python modules, which the "tests/" directory is not. Since tox calls all commands directly
-    # (which is good) file globbing doesn't work. To make file globbing work they need to be wrapped
-    # in a bash call (which is bad).
-    bash -c "reorder-python-imports {toxinidir}/tests/*.py --unclassifiable-application-module tox_poetry_installer"
-    bash -c "pylint --rcfile {toxinidir}/.pylintrc {toxinidir}/tests/*.py"
-    bash -c "mypy --ignore-missing-imports --no-strict-optional {toxinidir}/tests/*.py"
+    pylint --rcfile {toxinidir}/.pylintrc {toxinidir}/tests/
+    mypy --ignore-missing-imports --no-strict-optional {toxinidir}/tests/
 
 [testenv:security]
 description = Security checks