Added --server-type argument to Ruby cross-tests integration server

[kpumuk]

While working on #3307, I wanted to test Nonblocking server with cross tests and notice that Ruby integration test server does not support server type selection. C++ adds --server-type argument, and Python accepts it as positional.

This change adds --server-type and allows to run cross tests with different server types.

Unsurprisingly, cross-tests passed for framed transport and failed for buffered: https://github.com/kpumuk/thrift/actions/runs/22001432085/job/63575905711 (which is not compatible with nonblocking server).

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