Spotless spaceless self-closing rule conflicts with `maven-release-plugin`'s POM output, breaking release deploys

[khatchad]

Cutting 0.47.0 surfaced a release-breaking conflict between the Spotless self-closing-tag rule (#535, ponder-lab#351) and the maven-release-plugin.

Problem

ponder-lab#351 pins the spaceless self-closing form (<tag/>) via a Spotless replaceRegex, and its commit message states this "matches the maven-release-plugin's native output." That premise is incorrect. maven-release-plugin 3.3.1 re-serializes the root pom.xml during the version bump and emits the spaced form (<tag />):

• base master: <argLine/>
• [maven-release-plugin] prepare release 0.47.0 commit: <argLine />

So every release commit is Spotless-dirty on the root POM, in direct conflict with the enforced style.

Why it now breaks deploys

Previously this was only a master-hygiene nuisance, patched after the fact (e.g. c3d3d51e, "Apply spotless to pom.xml after release-plugin rewrite"), because the old ml-X.Y.Z tags failed the semver deploy gate and skipped deploy anyway. After ponder-lab#349 pinned tagNameFormat to plain X.Y.Z, the tag-push deploy actually runs — and its build job fails at "Check formatting with Spotless" on the dirty POM, so release-upload is skipped and the version never publishes via CI. 0.47.0 had to be deployed manually.

Suggested fix

Reconcile the two so releases produce Spotless-clean POMs with no manual step. Since maven-release-plugin owns POM serialization and emits the spaced form, the simplest fix is to exclude pom.xml from the spaceless self-closing enforcement (keep enforcing it on the summary XMLs like tensorflow.xml, where #351's normalization is valuable and nothing else rewrites them). Alternatively, automate spotless:apply into the release flow so both the release commit and the tag are clean.

Surfaced while releasing ponder-lab/ML 0.47.0 (the #539 fix).