Fails to build on Windows ARM64

The project fails to build on Windows ARM64, it does not contain the definition of maxMmapSize for given platform.

```
Error: ../../../go/pkg/mod/github.com/akrylysov/pogreb@v0.10.2/fs/os_mmap_windows.go:23:13: undefined array length maxMmapSize or missing type constraint
```

https://github.com/akrylysov/pogreb/blob/main/fs/os_mmap_windows.go#L23