Fix the Java formatting violations spotless reports

[maxjivi05]

GcmRumbleMode.java was stored with CRLF line terminators; the other three had @nullable on its own line, which the configured formatAnnotations() step folds onto the declaration.

Whitespace only, no semantic change. Verified with javac.

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[maxjivi05]

Code looks solid. No critical issues found.

This PR is whitespace-only: it folds @Nullable (and @Nullable @Override) onto the declaration line per the configured formatAnnotations() Spotless step, and normalizes GcmRumbleMode.java from CRLF to LF line endings. No logic, control flow, save/cloud-state, threading, or public API changes are present in the diff — reviewed against all 6 pillars (data integrity, concurrency, performance, controller accessibility, Android/C++ standards, test coverage), none of which apply here since no functional code changed.

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