fix: make isExtensionUpdateRequired uniformly public (widen over narrow)

[joaodinissf]

Problem

AbstractCheckExtensionHelper.isExtensionUpdateRequired is declared protected (a template-method hook, called only from the helper's own update flow), but five of its six subclasses have overridden it as public since the initial Check contribution (2016, e78f8113a) — Java permits an override to widen visibility, so the mismatch compiles silently. CheckMarkerHelpExtensionHelper is the lone protected override. The hierarchy carries two visibilities for one contract.

The trade-off, and the choice made

Two consistent end states were possible:

• Narrow the public outliers to protected, matching the parent declaration. This is the textbook template-method shape — but CheckTocExtensionTest and CheckContextsExtensionTest have unit-tested the hook directly on injected helper instances since 2017, from a different bundle and package. Narrowing breaks those calls and forces test-only re-widening subclasses (~24 lines of scaffolding whose sole job is to undo the narrowing for tests).
• Widen the parent declaration and the one remaining protected override to public. Two lines, no scaffolding, and it ratifies how the hierarchy has actually been designed and used for nine years: the predicate was evidently meant to be white-box testable from day one.

Widening was chosen — direct testability of the hook is a long-standing, deliberate part of this hierarchy's design, and the project generally accepts public where tests require it.

What this does

• AbstractCheckExtensionHelper.isExtensionUpdateRequired: protected → public.
• CheckMarkerHelpExtensionHelper.isExtensionUpdateRequired: protected → public (an override may not be narrower than its parent, so this follows necessarily).

Coordination note: #1397's helper refactor originally declared the two delegating overrides (CheckValidatorExtensionHelper, CheckQuickfixExtensionHelper) protected; it has been amended to keep them public so the build stays green in either merge order.

Verification

• Repo-wide caller census: the only callers of isExtensionUpdateRequired are the parent's own update flow, CheckMarkerHelpExtensionHelper's super call, and the two tests — no behavior change is possible; this is a visibility-only change.
• Full local gate (clean verify checkstyle:check pmd:pmd pmd:cpd pmd:check pmd:cpd-check spotbugs:check): BUILD SUCCESS.

🤖 Generated with Claude Code