Support connect_timeout keyword arg in TCPSocket

[rwstauner]

Accept the connect_timeout keyword argument to TCPSocket.new
and wrap the connect call with Timeout.timeout when provided.

closes #3421

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[eregon]

(I'm asking to add both to the existing Shopify OCA)

[eregon]

It looks great, thank you.
Just one comment.

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[eregon]

I am not sure why, but tests/specs related to connect_timeout fail transiently quite frequently.
e.g.:

1)
TCPSocket#initialize raises IO::TimeoutError with :connect_timeout when no server is listening on the given address ERROR
IO::TimeoutError: execution expired
/b/b/e/main/spec/ruby/library/socket/tcpsocket/shared/new.rb:30:in `block (3 levels) in <top (required)>'
/b/b/e/main/spec/ruby/library/socket/tcpsocket/initialize_spec.rb:5:in `<top (required)>'

Also one of the MRI tests.