buffer update opt: refactor UboManager and introduce FenceManager

[show50726]

The refactoring contains two parts: FenceManager and reallocation logic

FenceManager

This refactor extracts fence management logic from UboManager into a separate FenceManager class for better testability/readability. But the downside of this approach is that whenever we add a new synchronous backend API, we will need to add a corresponding MOCK_FUNCTION in MockDriver.h file. Otherwise, the compilation fails.

Reallocation Logic

Additionally, this refactors the UboManager allocation logic into two separate functions: allocateOnDemand and allocateAllInstances.
The allocateOnDemand function now implements a two-pass strategy:

1. First, it allocates slots for new material instances (those that have never been allocated).
2. Second, it allocates slots for existing instances that need to orphan their current allocation.

This specific order allows for a more accurate calculation of the required UBO size, which helps prevent multiple, cascading reallocations.

[pixelflinger]

my only comment here is that FenceManager is not really a generic, reusable class right? It's very much part of UboManager. Maybe you can make it an internal class of UboManager?