Add distributed server implementation and protocol definitions

- Introduced `protocol.py` for shared data models used in server/client communication, including request and response schemas for registration, job submission, and status updates.
- Implemented `server.py` to manage a SQLite job queue and client registry, handling job polling, status updates, and job completion.
- Created a cheat sheet for server usage, detailing commands for starting the server, submitting jobs, and monitoring clients.
- Added several experiment configuration files for various training setups, including geometry vector injections and baseline ensembles.

v4/distributed/hypertower-server.service

@@ -0,0 +1,17 @@
+[Unit]
+Description=HyperTower distributed job server
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=simple
+WorkingDirectory=/home/rpotter/hypertower
+Environment=HT_TOKEN=hypertower
+ExecStart=/home/rpotter/miniconda3/envs/fundus_imaging/bin/python -m v4.distributed.server --host 0.0.0.0 --port 8765
+Restart=on-failure
+RestartSec=5
+StandardOutput=journal
+StandardError=journal
+
+[Install]
+WantedBy=default.target