Adds the logical protocol layer on top of the frame codec: session
handshake with negotiated frame size, session scoped symbol handles,
state subscriptions with periodic, on change and deadband filtering,
command events with duplicate protection and continuous controls with
stale update rejection, plus per connection rate limits and diagnostics.
A single worker thread owns all of the blocking transport work and
exchanges finished frames with the simulation thread through short locked
queues, so a stalled, flooding or unplugged controller cannot hold up the
simulation.
Adds the transport-independent core of the MaSzyna Hardware Protocol v2:
COBS framing with a CRC32C protected 24 byte header, bounds checked
payload readers and writers, and a resynchronising stream decoder.
The shared TrainState registry describes simulator state in engineering
units with per-value quality, the command registry generates the command
namespace from Commands_descriptions, and the symbol registry merges both
into the public, name-addressed hardware api.
