bug: apply request_timeout to timeout_connect

[mtopolnik]

ureq has a potential bug in its agent builder code regarding timeouts. There are two kinds of timeout:

• agent_builder.timeout_connect() applies to establishing the TCP connection
• agent_builder.timeout() applies to the overall HTTP request
• timeout_connect is always applied for the connection phase, even if longer than the overall timeout
• timeout_connect has a default of 15 seconds
• it's impossible to revert timeout_connect to unconfigured state
• therefore, any timeout setting shorter than timeout_connect is basically ignored

This PR applies a workaround and sets timeout_connect to QuestDB's parameter request_timeout.

This partially addresses https://github.com/questdb/py-questdb-client/issues/75.

Also addresses #66.