[fix][client] Fix ServerSideErrorException when PulsarAdminUtils#getConsumeStats reads a markDeletePosition

[StevenLuMT]

Motivation

PulsarAdminUtils#getConsumeStats may fail with PulsarAdminException.ServerSideErrorException when a subscription's markDeletePosition advances to a newly rolled-over ledger that has no confirmed entries yet.

In this case, attempting to read the message at the consumed position can fail with a LastConfirmedEntry error. Similar boundary cases, such as a missing message or missing broker entry metadata index, should not cause the whole consume-stats query to fail.

Modifications

1. Clamp consumedMessageId to maxMessageId (lastConfirmedEntry) before reading its index.
2. Handle NotFoundException and ServerSideErrorException from getMessageById as no-valid-index cases.
3. Return -1 consistently when:
   • the target message is not readable;
   • the message does not exist;
   • the message has no index;
   • the position points to an empty newly rolled-over ledger.
4. Preserve the -1 sentinel value when converting a ledger-boundary position, avoiding an incorrect -2 offset.
5. Add warning logs for degraded consume-stats lookup paths.

Verifying this change

This change can be verified by running the existing CI checks.

The expected behavior is that getConsumeStats returns -1 for an unavailable consumed-message index instead of throwing an exception when the markDeletePosition points to a ledger with no confirmed entries.