Add messages: transponder navigation, modem ACKs

Breaking Changes

• Requires pyacomms >= 2.5

New Features

• Adds new messages that correspond to modem messages (published by acomms_driver_node):
  • NST ($CANST, Nav stats)
  • PDT ($SNPDT, Ping Digital Transponder Response)
  • PGT ($SNPGT, Ping Generic Transponder Response)
  • TTA ($SNTTA, Narrowband Transponder Ping Response)
  • ModemAck ($CAACK, Legacy ACK, and $CACDR, FDP Ack)
• acomms_driver_node publishes a std_msgs/Time message when $CAREV messages are received (sometimes used as a heartbeat)

Bugfixes

• Fixed the order of pip installs when doing gitlab-based tests.

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