chore: add mypy type checking

[fbessou]

No description provided.

[github-actions]

Unit tests Coverage

File	Stmts	Miss	Cover	Missing
__init__.py	0	0	100%
__main__.py	43	23	46%	17–18, 25, 52–53, 55, 57, 63–67, 71–80, 84
application.py	36	25	30%	19–22, 25, 28–30, 32–35, 39–43, 46–53
config.py	40	1	97%	48
events.py	18	0	100%
mapping.py	33	11	66%	33, 36–42, 45, 48, 55
pulse_worker.py	40	14	65%	13, 25–27, 42, 45, 48–55
repo_synchronizer.py	42	6	85%	29, 45–48, 65
TOTAL	252	80	68%

JUnit Xml Summary

Tests	Skipped	Failures	Errors	Time
7	2 💤	0 ❌	0 🔥	1.361s ⏱️

[github-actions]

Integration tests Coverage

File	Stmts	Miss	Cover	Missing
__init__.py	0	0	100%
__main__.py	43	14	67%	17–18, 25, 71–80, 84
application.py	36	4	88%	47–48, 52–53
config.py	40	1	97%	48
events.py	18	0	100%
mapping.py	33	2	93%	37, 41
pulse_worker.py	40	1	97%	13
repo_synchronizer.py	42	6	85%	29, 45–48, 65
TOTAL	252	28	88%

JUnit Xml Summary

Tests	Skipped	Failures	Errors	Time
7	0 💤	0 ❌	0 🔥	1.918s ⏱️