Split memory provider ops to mandatory and optional fields

[vinser52]

Description

As we agreed on our sync, the memory provider ops structure is split into mandatory and optional fields. Mandatory fields should be always initialized with a pointer to the appropriate function. Optional fields can be NULL. If an optional field is NULL the UMF initializes it with a default implementation that returns UMF_RESULT_ERROR_NOT_SUPPORTED error code.

Checklist

• Code compiles without errors locally
• All tests pass locally
• CI workflows execute properly

• New tests added, especially if they will fail without my changes