C++ target: Downcast warning on x32 in PredictionContextMergeCacheOptions.h

- Antlr4 v4.13.0
- Target: C++
- Visual Studio 2022

Compilation of `atn\PredictionContextMergeCacheOptions.h` on x32 system throws warning C4244 on line 51 (`getClearEveryN()`):
```
Conversion from "const uint64_t" to "size_t", possible loss of data.
```

Destination type is 32 bit, overflow may occur due to implicit cast.

Start with atn\PredictionContextMergeCacheOptions.h, especially getClearEveryN() at line 51, and reproduce the C4244 warning using the C++ target on a 32-bit build with Visual Studio 2022. Review the uint64_t-to-size_t conversion and verify the warning is gone without overflow-related behavior being introduced.

Written by the indexing model from the issue text.