Modifications to run lib on Windows

[prabhpreet]

Hello @CrabeDeFrance ,

Thanks for developing this crate. I attempted to use this on Windows but there were certain unix-specific dependencies present.

I had modified these to get this running on Windows 11. The tests passed locally on Windows. Please find and review this PR. Following are the changes:

• Added Unix specific #[cfg] directives in lib.rs for imports and tests using nix
• Modified test_rtshark_tshark_missing to remove "PATH" on starting of test and restore at end of test
• Added serialize_test crate as dev-dependencies in Cargo.toml to run test_rtshark_tshark_missing and test_rtshark_mutiple_spawn_pcap serially
• Modified dev-dependencies to only include nix package on Unix based systems in Cargo.toml

Best, Prabhpreet

[CrabeDeFrance]

Thanks for making it compatible with windows !