Consider some form of static analysis in CI

[LukeCarrier]

Following #59 we ought to extend our integration checks to cover oversights:

…/mkdocs-drawio-exporter on  HEAD (157dd90) is 📦 v0.9.0 via 🐍 v3.12.2
at 22:53:02 ✖ 1 🐠 ❯ asdf shell python 3.8.19

…/mkdocs-drawio-exporter on  main [⇣1] is 📦 v0.9.0 via 🐍 v3.8.19 took 3s 
at 22:53:12 🐠 ❯ g sw --detach v0.9.0
HEAD is now at 157dd90 Bump version to v0.9.0

…/mkdocs-drawio-exporter on  HEAD (157dd90) is 📦 v0.9.0 via 🐍 v3.8.19 
at 22:53:17 🐠 ❯ python -m flake8 mkdocs_drawio_exporter/
mkdocs_drawio_exporter/__init__.py:1:1: F401 '.exporter.DrawIoExporter' imported but unused
mkdocs_drawio_exporter/__init__.py:1:1: F401 '.exporter.Source' imported but unused
mkdocs_drawio_exporter/__init__.py:2:1: F401 '.plugin.DrawIoExporterPlugin' imported but unused
mkdocs_drawio_exporter/exporter.py:271:62: E999 SyntaxError: invalid syntax
mkdocs_drawio_exporter/plugin.py:52:61: E999 SyntaxError: invalid syntax
mkdocs_drawio_exporter/tests/__init__.py:1:1: F401 '.exporter.ExporterTests' imported but unused
mkdocs_drawio_exporter/tests/exporter.py:82:80: E501 line too long (95 > 79 characters)
mkdocs_drawio_exporter/tests/exporter.py:108:80: E501 line too long (87 > 79 characters)
mkdocs_drawio_exporter/tests/exporter.py:129:80: E501 line too long (109 > 79 characters)
mkdocs_drawio_exporter/tests/exporter.py:134:80: E501 line too long (96 > 79 characters)
mkdocs_drawio_exporter/tests/exporter.py:141:80: E501 line too long (82 > 79 characters)
mkdocs_drawio_exporter/tests/exporter.py:144:80: E501 line too long (90 > 79 characters)
mkdocs_drawio_exporter/tests/exporter.py:161:80: E501 line too long (113 > 79 characters)
mkdocs_drawio_exporter/tests/exporter.py:191:28: E711 comparison to None should be 'if cond is None:'
mkdocs_drawio_exporter/tests/exporter.py:207:80: E501 line too long (113 > 79 characters)
mkdocs_drawio_exporter/tests/exporter.py:219:28: E711 comparison to None should be 'if cond is None:'
mkdocs_drawio_exporter/tests/exporter.py:236:80: E501 line too long (113 > 79 characters)
mkdocs_drawio_exporter/tests/exporter.py:269:80: E501 line too long (108 > 79 characters)
mkdocs_drawio_exporter/tests/exporter.py:286:23: E712 comparison to False should be 'if cond is False:' or 'if not cond:'
mkdocs_drawio_exporter/tests/exporter.py:325:23: E711 comparison to None should be 'if cond is None: