Rename standard type Java package root

[nawforce]

Summary

• move generated platform stubs from com.nawforce.runforce to io.github.apexdevtools.standardtypes
• rewrite package declarations, imports, and fully-qualified references across the generated Java tree
• update repo generation guidance in .github/copilot-instructions.md to use the new package root

Testing

• mvn test
• mvn install -Dgpg.skip=true
• stale-reference sweep: no remaining com.nawforce.runforce / runforce references in this repo

Upstream impact

This is intentionally breaking for consumers that dynamically load classes by Java package name. A temporary apex-ls patch of PlatformTypeDeclaration.platformPackage and the Object$ import showed the next required change: apex-ls currently indexes standard-types and sobject-types into one Apex-facing name map, then loads everything through the platform package root. Because sobject-types still publishes under com.nawforce.runforce.SObjects, apex-ls either needs to retain the Java package root per indexed class or we need to migrate sobject-types to the same new root in a coordinated PR.