Make queue max read level always exclusive

[yycptt]

What changed?

• Currently the returned queue max read level is inclusive for immediate queue (transfer, visibility, replication) but exclusive for scheduled queue (timer).
• Follows the convention that a range is [inclusive, exclusive) and unify the behavior so that the returned max read level is always exclusive.

Why?

• Unify behavior.
• In multi cursor world, there's only one implementation of all queues (immediate or schedule) and if the interpretation of max read level is different, we need special logic in the queue impl to handle that.

How did you test it?

• existing test.
• local canary.

Potential risks

• in worst case, the last task in immediate queue can't be loaded.

Is hotfix candidate?

• no