Make sphinx works

A temporary solution, based on the following:

- introducing a new env variable ZINGG_DRY_RUN
- if the variable is set:
  + mimic globally used JVM-stuff
  + otherwise do nothing

++ slightly update ignore and docs/Makefile
++ apply formatting to client.py

 On branch 762-fix_sphinx_build
 Changes to be committed:
	modified:   .gitignore
	modified:   python/docs/Makefile
	new file:   python/pyproject.toml
	modified:   python/zingg/client.py

.gitignore

@@ -23,3 +23,10 @@ python/docs/_build/_doctrees
 **/python/build/*
 **/assembly/.classpath
 **/.DS_Store
+
+# Python stuff
+.env
+.venv
+
+# Sphinx _build
+**/_build

python/docs/Makefile

@@ -17,4 +17,6 @@ help:
 # Catch-all target: route all unknown targets to Sphinx using the new
 # "make mode" option.  $(O) is meant as a shortcut for $(SPHINXOPTS).
 %: Makefile
+	export ZINGG_DRY_RUN=1
 	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
+	unset ZINGG_DRY_RUN

python/pyproject.toml

@@ -0,0 +1,2 @@
+[tool.ruff]
+line-length = 150