Improve capacity calculation in FileMappedResizableDirectMemory constructor

**Location:** cpp/Platform.Memory/FileMappedResizableDirectMemory.h:35

**Current code:**
```cpp
// TODO: cringe
ReservedCapacity(size > minimumReservedCapacity ? ((size / minimumReservedCapacity) + 1) * minimumReservedCapacity : minimumReservedCapacity);
```

**Issue:**
The current capacity calculation logic needs improvement. The TODO comment indicates the current implementation is suboptimal.

**Suggestion:**
Review and refactor the capacity calculation logic to be more readable and potentially more efficient.

Start at cpp/Platform.Memory/FileMappedResizableDirectMemory.h:35 and inspect the current capacity calculation and its surrounding constructor context. Clarify the intended capacity behavior, then refactor the expression for readability or efficiency while preserving the required minimum capacity behavior; the issue is complete when the TODO is resolved and the constructor remains correct.

Written by the indexing model from the issue text.