EventFnArgMismatch fix to support defaults args

[LeoGrosjean]

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Type of change

• Bug fix (non-breaking change which fixes an issue)

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try to figure out how to, started to edit test_chain_event but then I realised it was not testing what I was coding.... so no test :(

• Have you successfully ran tests with your changes locally?

  More info in issue 4003

[LeoGrosjean]

closes #4003

[LeoGrosjean]

Not sure about pertinence of my last commit, I did it to please darglint

from

def check_fn_match_arg_spec(fn: Callable, arg_spec: ArgsSpec):

to

def check_fn_match_arg_spec(fn: Callable | callable, arg_spec: ArgsSpec | Any):

But parent scope is

call_event_fn(fn: Callable, arg_spec: ArgsSpec)

And it uses same inputs, code has been split for functionnal reason

[adhami3310]

Thank you for your contribution! We will merge it after the tests pass ;)