Allow CallsiteParameterAdder to be pickled

[Lunderberg]

Summary

Prior to this commit, the CallsiteParameterAdder object could not be pickled. As a result, structlog configurations could not be propagated to subprocesses using pickle.dumps(structlog.get_config()). This commit updates the handlers in CallsiteParameterAdder._handlers to be free functions, rather than lambda functions, so that all class members can be pickled.

Closes #600

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[hynek]

Can you make the function names verbs please? (iow: _pathname → _get_pathname).

Changelog entry would be great too ("structlog.processors.CallsiteParameterAdder is now pickleable." + link here).

(oh and get the CI green too, pls 😇 – I think it's just missing type hints for the functions?)

[Lunderberg]

Can you make the function names verbs please?

Can do. I've updated each function name from FOO to _get_callsite_FOO.

Changelog entry would be great too

And updated. (Made the commit for the changelog yesterday, but forgot to push it.)

(oh and get the CI green too, pls 😇 – I think it's just missing type hints for the functions?)

Thank you on pointing me in the right direction. Updated the signatures from (module, frame_info) to (module: str, frame_info: inspect.Traceback) to match the existing type annotation for CallsiteParameterAdder._handlers.

[hynek]

Great, thanks!