build: Drop support for Python 3.8

[matthewfeickert]

Description

Pulling in parts of PR #2566

• Support Python 3.9+, dropping support for Python 3.8.
• Simplify code by removing components that existed to support pre Python 3.9
  features or solutions.
• Use improved typing features from Python 3.9.
• Remove importlib_resources conditional dependency for Python < 3.9.
• Remove Python 3.8 trove classifier.
• Use Python 3.10 for the mypy minimum python check, due to Numpy typing being improved in 3.10+.

Checklist Before Requesting Reviewer

• Tests are passing
• "WIP" removed from the title of the pull request
• Selected an Assignee for the PR to be responsible for the log summary

Before Merging

For the PR Assignees:

• Summarize commit messages into a comprehensive review of the PR

* Support Python 3.9+, dropping support for Python 3.8.
* Simplify code by removing components that existed to support pre Python 3.9
  features or solutions.
* Use improved typing features from Python 3.9.
* Remove importlib_resources conditional dependency for Python < 3.9.
* Remove Python 3.8 trove classifier.
* Use Python 3.10 for the mypy minimum python check, due to Numpy typing being
  improved in 3.10+.

Co-authored-by: Giordon Stark <[email protected]>

[Copilot]

Pull Request Overview

This PR drops support for Python 3.8 and adopts Python 3.9+ features, simplifying the codebase by removing compatibility shims and leveraging improved typing capabilities.

Key changes:

• Removed conditional imports for importlib.resources (now always available in Python 3.9+)
• Updated type hints to use built-in generic types (list, tuple, set) and moved abstract types (Sequence, Mapping) from typing to collections.abc
• Simplified archive validation logic in contrib/utils.py to use direct is_tarfile/is_zipfile checks instead of try-except pattern

Reviewed Changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/contrib/test_viz.py	Removed Python 3.8 version check xfail decorator
src/pyhf/utils.py	Removed conditional import for importlib_resources
src/pyhf/typing.py	Updated to use built-in generics and collections.abc imports
src/pyhf/tensor/numpy_backend.py	Added type ignore comment and cast for improved type checking
src/pyhf/schema/variables.py	Removed conditional import for importlib_resources
src/pyhf/schema/validator.py	Moved Mapping import to collections.abc
src/pyhf/schema/loader.py	Removed conditional import for importlib_resources
src/pyhf/readxml.py	Updated type hints to use built-in generics and collections.abc
src/pyhf/pdf.py	Changed List[bool] return type to list[bool]
src/pyhf/parameters/paramsets.py	Changed List[bool] return type to list[bool]
src/pyhf/modifiers/staterror.py	Changed List[bool] parameter type to list[bool]
src/pyhf/mixins.py	Moved Sequence import to collections.abc
src/pyhf/contrib/utils.py	Refactored archive validation from try-except to if-elif-else structure
pyproject.toml	Updated minimum Python version to 3.9 and removed 3.8 classifier
.pre-commit-config.yaml	Updated mypy checks from Python 3.8 to 3.10
.github/workflows/release_tests.yml	Removed Python 3.8 from test matrix
.github/workflows/lower-bound-requirements.yml	Updated minimum Python version from 3.8 to 3.9
.github/workflows/ci.yml	Removed Python 3.8 from CI test matrix

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[matthewfeickert]

@kratsg this PR is mostly just a cherry-pick from your first commit in PR #2566, but to get Python 3.10 typing with mypy to pass I had to cast the output of transpose to ArrayLike.

I'm not sure if this makes sense or not, so I think you'll need to weigh in here.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.23%. Comparing base (2af4dea) to head (595ca57).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2625      +/-   ##
==========================================
- Coverage   98.23%   98.23%   -0.01%     
==========================================
  Files          65       65              
  Lines        4198     4190       -8     
  Branches      592      452     -140     
==========================================
- Hits         4124     4116       -8     
  Misses         45       45              
  Partials       29       29              

Flag	Coverage Δ
contrib	98.11% <100.00%> (+0.13%)	⬆️
doctest	98.23% <100.00%> (+0.13%)	⬆️
unittests-3.10	96.42% <86.36%> (+0.13%)	⬆️
unittests-3.11	96.42% <86.36%> (+0.13%)	⬆️
unittests-3.12	96.42% <86.36%> (+0.13%)	⬆️
unittests-3.13	96.42% <86.36%> (+0.13%)	⬆️
unittests-3.8	?
unittests-3.9	96.46% <90.90%> (+0.13%)	⬆️

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