Add producer wait strategies for capacity backoff

[svrohith9]

Summary

• add producer-side wait strategy API and implementations
• wire producer backoff into single/multi sequencers
• add RingBuffer/Disruptor overloads and docs updates
• add unit tests for producer wait strategies

Testing

• ./gradlew test

[adacooke]

Hi,
Thank you for your PR! Can I ask what the intended use case is for this feature? Generally the ring buffer being full is a really bad case and I don't know what use case would require configuring how that is handled.

[svrohith9]

@adacooke Thanks! The goal isn’t to normalize the full buffer. Those are still a bad sign. But brief
ring‑full periods do happen (bursts, GC pauses, downstream hiccups). Today producers always
parkNanos(1), which hard‑codes one latency/CPU tradeoff. This change just lets apps choose a
different backoff policy for those short contention windows. Default behavior stays the same.