ci: Set up Python-focused testing infra

.codecov.yml

@@ -0,0 +1,54 @@
+---
+
+codecov:
+  notify:
+    after_n_builds: 21  # Number of test matrix+lint jobs uploading coverage
+    wait_for_ci: false
+
+  require_ci_to_pass: false
+
+  token: >-  # notsecret  # repo-scoped, upload-only, stability in fork PRs
+    7316089b-55fe-4646-b640-78d84b79d109
+
+comment:
+  require_changes: true
+
+coverage:
+  range: 100..100
+  status:
+    patch:
+      default:
+        target: 100%
+      pytest:
+        target: 100%
+        flags:
+        - pytest
+      typing:
+        flags:
+        - MyPy
+    project:
+      default:
+        target: 95%
+      lib:
+        flags:
+        - pytest
+        paths:
+        - src/
+        target: 100%
+      tests:
+        flags:
+        - pytest
+        paths:
+        - tests/
+        target: 100%
+      typing:
+        flags:
+        - MyPy
+        target: 90%
+
+github_checks:
+  # Annotations are deprecated in Codecov because they are misleading.
+  # Ref: https://github.com/codecov/codecov-action/issues/1710
+  annotations: false
+
+...

.coveragerc

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+[html]
+show_contexts = true
+skip_covered = false
+
+[paths]
+_site-packages-to-src-mapping =
+  src
+  */src
+  *\src
+  */lib/pypy*/site-packages
+  */lib/python*/site-packages
+  *\Lib\site-packages
+
+[report]
+skip_covered = true
+skip_empty = true
+show_missing = true
+exclude_also =
+  ^\s*@pytest\.mark\.xfail
+  ^\s*\.\.\.\s*(#.*)?$
+
+[run]
+branch = true
+cover_pylib = false
+# https://coverage.rtfd.io/en/latest/contexts.html#dynamic-contexts
+# dynamic_context = test_function  # conflicts with `pytest-cov` if set here
+parallel = true
+plugins =
+  covdefaults
+relative_files = true
+source =
+  .
+source_pkgs =
+  pre_commit_terraform