This fix properly handles case when destination server returns an invalid
or malformed http response, preventing mmar client from crashing and informing
the user to check the destination server's logs.

Checks if mmar config flags are set in env variables if
not passed into cli flags. Otherwise fallback to defaults.

These flags allow users to configure a custom DNS or TLS certificates
for the mmar client to use when making request to the dev server.

They are mainly used in simulation tests, however they could be utilized
in more complicated setups.

This allows for cleaner separation between when tcp connections
are created and when perform tunnel actions such as creating or
reclaiming existing tunnels.

This commit implements tcp multiplexing which significantly improves
the performance and experience of make requests through mmar tunnels.
It now supports processing multiple requests/responses concurrently
on the same single TCP connection between mmar server and client.