Match Spotless POM self-closing style to maven-release-plugin output

[khatchad]

Fixes the release-breaking Spotless conflict that forced 0.47.0 to be deployed manually (wala#566).

Problem

maven-release-plugin re-serializes POMs with the spaced self-closing form (<tag />) during release:prepare, but Spotless's sortPom enforced the spaceless form (<tag/>). So every release commit was Spotless-dirty on the root POM. Pre-wala/ML#349 this was harmless (the ml-X.Y.Z tags failed the semver deploy gate and skipped deploy anyway, with post-hoc cleanup like c3d3d51e). After #349 pinned plain X.Y.Z tags, the tag-push build job fails at spotless:check and silently skips release-upload — 0.47.0 never published via CI and had to be deployed by hand.

Note this is not the conflict wala#351 addressed: POMs are already excluded from #351's replaceRegex. The POM conflict is sortPom's, and #351's premise that the spaceless form "matches the maven-release-plugin output" was incorrect — the plugin emits the spaced form.

Fix

Set sortPom's spaceBeforeCloseEmptyElement=true so Spotless enforces the same spaced form the release plugin emits. Release commits are now clean from the start. Only POMs adopt the spaced form; the summary XMLs (tensorflow.xml, etc.) stay spaceless via the separate replaceRegex step (wala#535), since nothing rewrites them.

Verification

A release:prepare -DdryRun produces a tag POM that is formatting-identical to the Spotless-clean committed POM — the only differences are the <version> and scm <tag> values:

6c6
<   <version>0.47.1-SNAPSHOT</version>
> <version>0.99.0</version>
22c22
<     <tag>ml-0.45.0</tag>
> <tag>0.99.0</tag>

So a real release will pass the tag build's spotless:check and deploy without manual intervention.

Fixes wala#566.

[Copilot]

Pull request overview

Aligns Spotless POM formatting with maven-release-plugin’s POM serialization so release:prepare no longer produces release commits that immediately fail spotless:check, unblocking CI-driven releases.

Changes:

• Configure Spotless sortPom to emit spaced self-closing tags (<tag />) via spaceBeforeCloseEmptyElement=true.
• Normalize existing self-closing tags in pom.xml to the spaced form to match the new formatter behavior.
• Add explanatory documentation in pom.xml linking the change to the release failure scenario (wala#566).

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.29%. Comparing base (d70fad6) to head (391b36b).

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #356   +/-   ##
=========================================
  Coverage     71.29%   71.29%           
  Complexity     2674     2674           
=========================================
  Files           270      270           
  Lines         20152    20152           
  Branches       3257     3257           
=========================================
  Hits          14367    14367           
  Misses         4487     4487           
  Partials       1298     1298           

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