Add ForbiddenPublicSealedClass detekt rule

[tonidero]

Summary

• Adds a new :detekt-rules Gradle module with a custom ForbiddenPublicSealedClass detekt rule
• The rule flags public sealed class and public sealed interface declarations in non-example paths, unless annotated with @InternalRevenueCatAPI
• Mirrors the existing ForbiddenPublicDataClass enforcement pattern from detekt-rules-libraries
• Pre-existing violations (intentionally public sealed types already in the SDK) are added to the detekt baseline
• The rule correctly ignores sealed classes nested inside internal classes (e.g. SubscriberAttributeKey subtypes)

Why: Adding a new subclass to a public sealed class/interface is a binary-incompatible change — any exhaustive when in consumer code breaks at runtime. Catching this at lint time prevents accidental API breakage.

Baselined pre-existing violations (to be addressed in follow-up PRs if needed):

• AmazonPurchasingData, GalaxyPurchasingData, GooglePurchasingData
• RedeemWebPurchaseListener.Result
• PaywallResult, PaywallFont, PurchaseLogicResult
• Purchases.DeepLink (custom entitlement computation variant)

Test plan

• ./gradlew detektAll passes with no new violations
• Adding a new public sealed class without @InternalRevenueCatAPI in purchases/src/main/kotlin/ causes detektAll to fail
• Adding @InternalRevenueCatAPI to that class suppresses the violation
• Classes nested inside internal classes are not flagged

🤖 Generated with Claude Code

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	maven/​io.gitlab.arturbosch.detekt/​detekt-api@​1.23.6 ⏵ 1.23.8	+6

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.89%. Comparing base (8d7b612) to head (add8da2).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3503   +/-   ##
=======================================
  Coverage   79.89%   79.89%           
=======================================
  Files         369      369           
  Lines       14871    14871           
  Branches     2048     2048           
=======================================
  Hits        11881    11881           
  Misses       2157     2157           
  Partials      833      833           

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