[server] Switch back to PubSubPosition based reads with offset as fallback

[sushantmane]

Switch back to PubSubPosition based reads with offset as fallback

Code changes

• [ ] Added new code behind a config. If so list the config names and their default values in the PR description.
• [ ] Introduced new log lines.
  • [ ] Confirmed if logs need to be rate limited to avoid excessive logging.

Concurrency-Specific Checks

Both reviewer and PR author to verify

• [ ] Code has no race conditions or thread safety issues.
• [ ] Proper synchronization mechanisms (e.g., synchronized, RWLock) are used where needed.
• [ ] No blocking calls inside critical sections that could lead to deadlocks or performance degradation.
• [ ] Verified thread-safe collections are used (e.g., ConcurrentHashMap, CopyOnWriteArrayList).
• [ ] Validated proper exception handling in multi-threaded code to avoid silent thread termination.

How was this PR tested?

• [ ] New unit tests added.
• [ ] New integration tests added.
• [ ] Modified or extended existing tests.
• [ ] Verified backward compatibility (if applicable).

Does this PR introduce any user-facing or breaking changes?

• [ ] No. You can skip the rest of this section.
• [ ] Yes. Clearly explain the behavior change and its impact.