Fix max iters issue and add tests

[goanpeca]

Fixes #1521

Depends on:

• Add typing and style checks as separate workflows #3442
• Add fixes to doctest and fix incorrect link #3443
• Fix MPS #3444
• Fix codecov deprecation warning #3445

[Copilot]

Pull Request Overview

This PR implements a fix for max_iters handling in the Engine state dictionary and adds comprehensive test coverage. The changes extend the Engine class to properly support max_iters as an alternative to max_epochs for controlling training duration.

Key changes include:

• Enhanced Engine state dict validation to support both max_epochs and max_iters termination modes
• Updated serialization logic to include appropriate termination parameters based on the training configuration
• Extended test coverage for various max_iters scenarios including resuming, state loading, and edge cases

Reviewed Changes

Copilot reviewed 21 out of 21 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
tests/ignite/engine/test_max_iters_fix.py	Comprehensive test suite for max_iters functionality covering state dict operations, resuming, and validation
tests/ignite/engine/test_engine_state_dict.py	Updated existing tests to account for additional state dict keys
tests/ignite/conftest.py	Added defensive checks for pytest configuration options
tests/ignite/base/test_mixins_update.py	Tests for updated Serializable mixin validation logic
ignite/engine/engine.py	Core Engine implementation with max_iters support and improved state management
ignite/base/mixins.py	Enhanced Serializable base class with grouped optional key validation
Various workflow and metric files	Minor fixes and updates

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[vfdev-5]

Thanks a lot for the PR @goanpeca !
I made the first pass and left comments essentially to split this PR into multiple ones and explain certain changes.
I'll check in more depth the max_iters related changes a bit later whether it works as expected.
Anyway, great job!