fix(typing): Make event processor types consistent

[alexander-alderman-webb]

Some of the event processors in our integrations have a return type of Event when they never return None, while others keep the more general Optional[Event]. Returning Event where possible allows us to see at a glance that the event processors set by the integration cannot drop an event.

Also make use of the EventProcessor in a few more places.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.57%. Comparing base (94a92d8) to head (9d333e1).
⚠️ Report is 5 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4789      +/-   ##
==========================================
+ Coverage   84.55%   84.57%   +0.02%     
==========================================
  Files         158      158              
  Lines       16479    16479              
  Branches     2855     2855              
==========================================
+ Hits        13933    13937       +4     
+ Misses       1700     1695       -5     
- Partials      846      847       +1     

Files with missing lines	Coverage Δ
sentry_sdk/integrations/arq.py	95.04% <ø> (ø)
sentry_sdk/integrations/asgi.py	90.64% <ø> (ø)
sentry_sdk/integrations/aws_lambda.py	29.00% <ø> (ø)
sentry_sdk/integrations/dramatiq.py	83.75% <ø> (ø)
sentry_sdk/integrations/fastapi.py	89.02% <ø> (ø)
sentry_sdk/integrations/gcp.py	0.00% <ø> (ø)
sentry_sdk/integrations/huey.py	97.46% <ø> (ø)
sentry_sdk/integrations/spark/spark_driver.py	66.26% <ø> (ø)
sentry_sdk/integrations/spark/spark_worker.py	82.14% <ø> (ø)
sentry_sdk/integrations/starlette.py	85.02% <ø> (ø)

... and 2 files with indirect coverage changes

[alexander-alderman-webb]

Is this method considered public because there's no leading underscore?

[antonpirker]

An event processors return type must be Optional[Event] because as how event processors work, you either return an (optionally updated) event or you return None which means the event will be dropped.

[alexander-alderman-webb]

Why does an event processor need to return Optional[Event] if there are no code paths where the event is dropped from the specific event processor? Currently in the SDK we have event processors typed like this:

sentry-python/sentry_sdk/integrations/fastapi.py

Lines 114 to 117 in dcefe38

	def _make_request_event_processor(req, integration):
	# type: (Any, Any) -> Callable[[Event, Dict[str, Any]], Event]
	def event_processor(event, hint):
	# type: (Event, Dict[str, Any]) -> Event

I'm happy to close the PR if it breaks anything since it's just meant to improve readability.