refactor(bump): use VersionIncrement ordering for bump detection

[bearomorphism]

Description

This PR extracts the find_increment removal from the larger BumpRule redesign by replacing it with comparable VersionIncrement helpers and shared max-based increment selection.

It keeps the current bump_pattern / bump_map behavior intact, including:

• filtered commits before bump/version calculation
• major_version_zero
• legacy invalid custom-map failures
• existing no-increment semantics

Checklist

• I have read the contributing guidelines

Was generative AI tooling used to co-author this PR?

• Yes (Pi / no-mistakes)

Generated-by: Pi / no-mistakes following http://commitizen-tools.github.io/commitizen/contributing/pull_request/#ai-assisted-contributions

Code Changes

• Add test cases to all the changes you introduce
• Run uv run poe all locally to ensure this change passes linter check and tests
• Manually test the changes:
  • Verify the feature/bug fix works as expected in real-world scenarios
  • Test edge cases and error conditions
  • Ensure backward compatibility is maintained
  • Document any manual testing steps performed
• Update the documentation for the changes

Documentation Changes

• Run uv run poe doc locally to ensure the documentation pages renders correctly
• Check and fix any broken links (internal or external)

Expected Behavior

cz bump and cz version --project --next USE_GIT_COMMITS should keep their existing bump-selection behavior after commitizen.bump.find_increment is removed, while internal increment selection now uses comparable VersionIncrement values.

A documented None / null bump_map value should also match the public typed plugin/config contract, while the string "NONE" remains invalid.

Steps to Test This Pull Request

1. Run the targeted regression suite for bump/version behavior.
2. Exercise cz bump and cz version --project --next USE_GIT_COMMITS in isolated repos covering invalid custom bump maps, multiline MAJOR handling, filtered commits, major_version_zero, and actual None bump-map values.
3. Confirm the current PR head passes GitHub checks.

Additional Context

• This PR was rewritten to a single commit after no-mistakes introduced intermediate fix commits during validation, then received one follow-up commit for the typed None bump-map contract.
• Local validation for the follow-up head passed: ruff check, ruff format --check, mypy, and targeted bump/version pytest coverage (223 passed).
• GitHub checks for the current head should be treated as the source of truth after the latest push.

[github-actions]

🔍 Commitizen bump preview

Merging this PR will produce the following bump:

bump: version 4.19.0 → 4.19.1
tag to create: v4.19.1
increment detected: PATCH

## v4.19.1 (2026-10-01)

### Fix

- **types**: allow documented None bump_map values

### Refactor

- **bump**: replace find_increment with VersionIncrement max

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.28%. Comparing base (3f5ccc8) to head (13cd81d).
⚠️ Report is 3 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2097      +/-   ##
==========================================
+ Coverage   98.27%   98.28%   +0.01%     
==========================================
  Files          61       61              
  Lines        2836     2861      +25     
==========================================
+ Hits         2787     2812      +25     
  Misses         49       49              

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

[bearomorphism]

Previous PR: #1518

This is smaller and the goal is to remove bump.find_increment first

[Copilot]

Copilot review overview

🟡 Changes recommended

The documented None mapping conflicts with the public bump-map type annotations.

Review effort: Balanced
Findings: 1

Open (1)

• Widen bump-map annotations to permit documented None values · New

What changed in this PR

Centralizes bump detection around ordered VersionIncrement values while preserving existing CLI behavior.

Changes:

• Replaces find_increment with shared increment helpers.
• Updates bump/version commands and regression coverage.
• Documents no-bump custom mappings.

File	Description
commitizen/​version_increment.py	Adds ordered increment extraction helpers.
commitizen/​bump.py	Removes legacy increment detection.
commitizen/​commands/​bump.py	Uses shared increment selection.
commitizen/​commands/​version.py	Reuses selection for commit-derived versions.
tests/​test_version_increment.py	Adds helper and compatibility tests.
tests/​test_bump_find_increment.py	Removes obsolete tests.
tests/​commands/​test_bump_command.py	Tests invalid custom mappings.
docs/​customization/​python_class.md	Documents None mappings.
docs/​customization/​config_file.md	Documents JSON/YAML null mappings.

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