Re-enable checkstyle enforcement

[devin-ai-integration]

Summary

checkstyle.fail.on.violation has been false since the JDK 21 refresh (walmartlabs#159), which reported ~157 (currently 316) javadoc violations as "pre-existing debt to fix separately". Almost none of it is real debt: the Checkstyle 10 migration dropped properties from the JavadocMethod module without replacing them, silently turning on @param/@return requirements the project never had. Restoring the original intent leaves 22 genuine violations, which are fixed here, so enforcement goes back on.

 <module name="JavadocMethod">
-    <property name="validateThrows" value="false"/>
+    <property name="accessModifiers" value="public"/>     <!-- was scope=public -->
+    <property name="allowMissingParamTags" value="true"/>
+    <property name="allowMissingReturnTag" value="true"/>
+    <property name="validateThrows" value="false"/>
+    <property name="allowedAnnotations" value="Override, Test, BeforeEach, ..."/>
 </module>

Compare against the rules as originally committed in c6c6bb4 — scope=public, allowMissingParamTags, allowMissingThrowsTags, allowMissingReturnTag, allowedAnnotations, etc. scope was renamed to accessModifiers; minLineCount, allowThrowsTagsForSubclasses and allowMissingPropertyJavadoc no longer exist and have no equivalent, but they only ever loosened the check further. allowedAnnotations is also updated for the JUnit 5 lifecycle annotation names.

That drops 316 → 22. The remainder are real and fixed individually:

• Stale @param names that no longer match the signature — @param transactionParsers on registerTransactionSetParser(TransactionSetParser txParser), likewise in AbstractTransactionSetParserChainable, and @param errorDetail → errorDetails in AbstractX12TransactionSetWithLoop.
• Two malformed @throws tags that made Checkstyle's javadoc parser bail on the whole comment (surfacing as confusing AtclauseOrder / JavadocTagContinuationIndentation parse errors): @throws @{link PatternSyntaxException} (a typo'd {@link) and @throws {@link X12ParserException}. @throws wants an exception name, not a link.
• One static-import ordering nit in SegmentIteratorTest.

The three RightCurly violations were all } while (...) closings, which cannot satisfy option=alone, so LITERAL_DO is dropped from that module's token list rather than reformatting valid do-while loops.

No behavior change — only javadoc text, one import reorder, and build config. Verified: mvn clean test → You have 0 Checkstyle violations. and 412 tests pass. I also confirmed the gate actually bites by temporarily adding a second top-level class, which fails the build with OneTopLevelClass.

Link to Devin session: https://app.devin.ai/sessions/5280d76c516144ad88d3910c89b9ab3b
Requested by: @AllenGithu8

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✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

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