Switch to PEP517 build with Hatch

[akx]

Refs #850 (since builds will always be PEP517).

I'm not sure if the build hook should automatically run import_cldr, since it's not completely free in terms of compute and bandwidth, but at least the hook will complain if the package-to-be-built will be broken. 🤔

I verified that a cherry-pick of this branch on https://github.com/python-babel/babel/releases/tag/v2.17.0 builds tarballs and wheels very much like the ones currently released on PyPI.

[codecov[bot]]

Codecov Report

:x: Patch coverage is 0% with 1 line in your changes missing coverage. Please review. :white_check_mark: Project coverage is 91.93%. Comparing base (fb1c19c) to head (4be08f3).

Files with missing lines	Patch %	Lines
babel/core.py	0.00%	1 Missing :warning:

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1226   +/-   ##
=======================================
  Coverage   91.93%   91.93%           
=======================================
  Files          27       27           
  Lines        4688     4688           
=======================================
  Hits         4310     4310           
  Misses        378      378           

Flag	Coverage Δ
macos-14-3.10	90.97% <0.00%> (ø)
macos-14-3.11	90.91% <0.00%> (ø)
macos-14-3.12	91.12% <0.00%> (ø)
macos-14-3.13	91.12% <0.00%> (ø)
macos-14-3.8	90.84% <0.00%> (ø)
macos-14-3.9	90.90% <0.00%> (ø)
macos-14-pypy3.10	90.97% <0.00%> (ø)
ubuntu-24.04-3.10	90.99% <0.00%> (ø)
ubuntu-24.04-3.11	90.93% <0.00%> (ø)
ubuntu-24.04-3.12	91.14% <0.00%> (ø)
ubuntu-24.04-3.13	91.14% <0.00%> (ø)
ubuntu-24.04-3.8	90.86% <0.00%> (ø)
ubuntu-24.04-3.9	90.92% <0.00%> (ø)
ubuntu-24.04-pypy3.10	90.99% <0.00%> (ø)
windows-2022-3.10	90.98% <0.00%> (ø)
windows-2022-3.11	90.92% <0.00%> (ø)
windows-2022-3.12	91.13% <0.00%> (ø)
windows-2022-3.13	91.13% <0.00%> (ø)
windows-2022-3.8	90.96% <0.00%> (ø)
windows-2022-3.9	90.91% <0.00%> (ø)
windows-2022-pypy3.10	90.98% <0.00%> (ø)

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