Fix: Linux Interop Issues for Custom Merge Operators

[Havret]

I ran into a classic "it works on my machine" scenario while working on the new Merge Operator support (see #42) for my RocksDb.Extensions wrapper library. My tests were green on macOS, but the Linux CI build was failing mysteriously.

After some digging, I realized the issue was in how we handled the success output parameter in the C# interop layer.

The underlying RocksDB native API expects the success indicator to be a boolean-like value (0 or 1) stored in an unsigned char*, but we were marshalling it as an IntPtr. While macOS was lenient with this, Linux was not having it.

I've updated the implementation to correctly marshal this as a byte, ensuring it works cross-platform.

Reference: RocksDB C Header definition

@theolivenbaum could you please take a look at this?

[theolivenbaum]

Looks good, thanks for the contribution! And yeah the header to native generation is sometimes not correct. I need to investigate another solution I used for a friend project that uses a compiler based pass to generate the bindings