Tests: Fix Clang warnings (-Wswitch, -Wdangling-else )

[MaciekChoszczyk]

1. When building the test suite (src/Tests.cpp) with Clang, the compiler reported several -Wswitch and -Wdangling-else diagnostic warnings.

2. Added missing default: assert(0); cases to eliminate -Wswitch warnings on unhandled enumeration values.

3. Added explicit scope braces in TestDefragmentationSimple() to resolve -Wdangling-else.

4. Built locally with Clang-CL: compiles cleanly with 0 warnings.

5. Ran the test suite: all runtime tests pass without assertion failures.

[sawickiap]

Thank you for this contribution. I merged it - to my fork for now:

https://github.com/sawickiap/VulkanMemoryAllocator