docs(sdks): document Java retry backoff schedule client options

[devin-ai-integration]

Summary

The generated Java SDK client builder exposes three runtime options controlling the exponential backoff schedule between retries, alongside the existing maxRetries. These are runtime builder methods on the generated client, not generators.yml config (verified against ICustomConfig.java, which only defines maxRetries), so they're documented on the canonical runtime retry page (Retries with backoff) rather than in configuration.mdx.

Added a ### Customizing the backoff schedule subsection to retries-with-backoff.mdx with a Java example and the three options + defaults:

• initialRetryDelayMillis (default 1000)
• maxRetryDelayMillis (default 60000)
• retryJitterFactor (default 0.2, between 0 and 1)

Available on both the root client builder and ClientOptions.Builder.

Also added an inline cross-reference from the maxRetries entry in the Java configuration.mdx (a generators.yml reference) to the new backoff section, so readers who land on the config page can find the runtime tuning options:

 The default number of retries for failed requests. ... SDK users can still override this
-per-request via request options.
+per-request via request options, and can tune the [backoff schedule between retries](...#customizing-the-backoff-schedule) at client instantiation.

Source: fern-api/fern#16973.

Link to Devin session: https://app.devin.ai/sessions/ebd4f54345f542ad8d0afa752122b2ee

[devin-ai-integration]

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[github-actions]

🌿 Preview your docs: https://fern-preview-devin-1783616990-java-retry-backoff-options.docs.buildwithfern.com/learn

Here are the markdown pages you've updated:

• learn/sdks/deep-dives/retries-with-backoff
• learn/sdks/generators/java/configuration