Add type annotations and fix some lint warnings in Python code

[cyyever]

Description

More robust type checking in Python.

Motivation and Context

For better code

[codecov]

Codecov Report

Attention: Patch coverage is 70.45455% with 13 lines in your changes missing coverage. Please review.

Project coverage is 57.23%. Comparing base (651d579) to head (edb7c6a).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
onnx/reference/ops/experimental/_op_list.py	38.88%	10 Missing and 1 partial ⚠️
.../reference/ops/aionnx_preview_training/_op_list.py	87.50%	0 Missing and 1 partial ⚠️
onnx/reference/ops/aionnxml/_op_list.py	85.71%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6473      +/-   ##
==========================================
- Coverage   57.23%   57.23%   -0.01%     
==========================================
  Files         507      507              
  Lines       31447    31437      -10     
  Branches     3543     3542       -1     
==========================================
- Hits        18000    17993       -7     
+ Misses      12597    12595       -2     
+ Partials      850      849       -1     

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[cyyever]

@justinchuby More fixes.

[justinchuby]

cc @xadupre for approval