Add tests and publish repository metadata for MIL-003

Add 19 pytest tests covering the report, resource check, coin
processing, refunds, change, profit, make_coffee and the main loop.
Add a tests package and put the project root on the pytest path.
Doxygen output is clean. The repository description and topics were set
on the git host.

Closes #13
Closes #14
Closes #15
Closes #16
Closes #17

Task: MIL-003#1
Task: MIL-003#2
Task: MIL-003#3
Task: MIL-003#4
Task: MIL-003#5

pyproject.toml

@@ -22,7 +22,7 @@ where = ["src"]
 
 [tool.pytest.ini_options]
 testpaths = ["tests"]
-pythonpath = ["src"]
+pythonpath = ["src", "."]
 
 [tool.ruff]
 line-length = 88