Show running games in Discord as Rich Presence

Watch /proc for Steam games (by app ID, from Steam's reaper process) and
other games (by executable, from Discord's detectable list), and report
the first one to Discord's IPC socket with the game's own app ID.

pyproject.toml

@@ -0,0 +1,13 @@
+[tool.ruff]
+line-length = 120
+
+[tool.ruff.lint]
+select = ["E", "F", "W", "I", "B", "UP"]
+
+[tool.mypy]
+files = ["discord_game_presence.py", "tests"]
+strict = true
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]
+pythonpath = ["."]