Shrink packet spec

[linguini1]

This PR introduces changes to the packet specification which drastically reduce packet sizes and control information per packet.

The changes to the packet header include:

• Removal of length and version fields
• Addition of 8-bit block count field which contains the number of blocks in the packet
• Shrink packet number to 8-bit rolling sequence number counter
• Addition of 16 bit unsigned timestamp in minutes since power-on

Other changes:

• Block header is just a single 8-bit type identifier
• Debug message type removed since it was never practically used
• Voltage ID field shrunk to 8 bit
• Measurement time is now a 16-bit field in milliseconds to be offset from the packet header timestamp measured in minutes. This allows millisecond precision for measurement times in less space, while also keeping the maximum mission length to 1092~ hours

[linguini1]

radio_packet_format.pdf

[EliasJRH]

Some small nits, everything else good.