lib/logging: Initialize handlers as Set instead of List

[adityagesh]

Handlers is currently initialized as empty list. The operation most performed is contains. Set performs faster for this and ordering of handler is not a concern. Hence replace the list initialization with set.

[ghost]

All commit authors signed the Contributor License Agreement.

[bedevere-app]

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

[ZeroIntensity]

Sorry, this is a breaking change. handlers is documented as a list: https://docs.python.org/3/library/logging.html#logging.Logger.handlers

[vsajip]

As pointed out, a breaking change.

Set performs faster for this

Did you do any benchmarks with realistic scenarios? Even if a set is faster, how much difference does it really make? I'm minded to close this.

[ZeroIntensity]

If it's a really significant speedup (which I doubt it is), then in theory we could deprecate handlers for a new attribute, and then just reflect changes to it for compatibility. I'm speculating though, and I'd definitely like to see some benchmarks before doing that.

[adityagesh]

I don't have benchmark at the moment. I'll close this for now and reopen when I have data.