docs: fix async pagination examples

[abhinavkr26104]

Summary

• replace CompletableFuture.thenRun with thenAccept in the async pagination README examples
• keep the page value available to call page.autoPager()

Problem

The examples passed a page -> ... lambda to thenRun. Java's CompletableFuture.thenRun accepts a zero-argument Runnable, so all three snippets failed to compile as documented.

Reproduction

1. Copy the async pagination examples from README.md into a Java source file.
2. Compile with the SDK dependencies.
3. The compiler rejects each pageFuture.thenRun(page -> ...) call because the lambda has an unexpected parameter.

Fix

Use thenAccept, whose Consumer<JobListPageAsync> receives the completed page.

Validation

• git diff --check
• Local Gradle compile/test attempts exceeded the command timeout without producing a compiler or test failure.

Fixes #849