fix(deps): drop pytz from dependencies

[romaingd]

Description of changes

Hi! This PR proposes dropping pytz from primary dependencies and replacing it with stdlib equivalents, as recommended by pytz docs:

Projects using Python 3.9 or later should be using the support now included as part of the standard library, and third party packages work with it such as tzdata. pytz offers no advantages beyond backwards compatibility with code written for earlier versions of Python.

Given that Ibis only supports Python 3.9 and higher, this should be pretty safe.

[romaingd]

This is not linked to pytz, but while testing changes in Flink backend I wondered why apache-flink was never installed, and it took me some time to find the explanation in #8696 (comment). I figured I might as well add a comment to save future readers some time. I can split it into a separate PR if deemed more appropriate.

[cpcloud]

Thank you. Yes, this is definitely a bit hairy at the moment and will be until the Flink team can support a later version of Arrow.

[romaingd]

From tzdata documentation on PyPI:

This is a Python package containing zic-compiled binaries for the IANA time zone database. It is intended to be a fallback for systems that do not have system time zone data installed (or don’t have it installed in a standard location), as a part of PEP 615

Unfortunately, without it Windows tests all fail due to a lack of TZ information.

[romaingd]

For reference, pandas uses "tzdata>=2022.7" as well

[cpcloud]

Is it safe to only install this on Windows (using a platform selector like sys_platform == 'win32')?

[romaingd]

It would be sufficient to cover the OS we test against (Ubuntu & MacOS have system TZ data, Windows would have the fallback), but I don't know if less popular OS / other Linux distributions come with system time zone data, so it's a bit of a gamble - one that I personally wouldn't take.

[cpcloud]

Small question about tzdata, but not blocking. Thanks for doing this!