Add Windows curl DLL names

[Watson1978]

Fixes #270

This PR resolves the LoadError on Windows by adding the missing DLL names to ffi_lib.

Currently, ethon only looks for libcurl and libcurl.so.4.
However, on modern Windows environments, the curl DLL is named differently depending on how it was installed:

1. MSYS2 (RubyInstaller default):
   • Installing via pacman -S mingw-w64-ucrt-x86_64-curl provides libcurl-4.dll.
2. Official curl for Windows:
   • Downloading the official binaries from curl.se provides architecture-specific names like libcurl-x64.dll and libcurl-arm64.dll.