annotate return types of a few functions to enable more mypy check

[tdadela]

Before (mypy checks in CI):

mypy: commands[0]> mypy locust/
locust/stats.py:209: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]
locust/stats.py:210: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]
locust/runners.py:600: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]
locust/runners.py:661: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]
locust/runners.py:663: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]
locust/runners.py:681: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]
locust/contrib/fasthttp.py:345: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]
locust/main.py:94: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]
locust/test/test_runners.py:947: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]

After:

mypy: commands[0]> mypy locust/
locust/stats.py:209: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]
locust/stats.py:210: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]
locust/main.py:94: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]
locust/test/test_runners.py:947: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]

The remaining 4 mypy notes requires more changes than just adding return types. (Fixing annotations inside functions.)

[cyberw]

👍 I’m considering switching to pyright. Do you have any opinion on that? Because it is so much faster it can be added as a precommit hook as well.

[tdadela]

My experience with both of them is limited, so unfortunately I can't share any useful thoughts.