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/classes/accessory/backbones.py

@@ -109,6 +109,12 @@ BACKBONES: Dict[str, BackboneSpec] = {
         strip=_strip_efficientnet,
         blocks=_blocks_efficientnet,
     ),
+    "resnet18": BackboneSpec(
+        ctor=models.resnet18,
+        weights_default=models.ResNet18_Weights.DEFAULT,
+        strip=_strip_resnet,
+        blocks=_blocks_resnet,
+    ),
     "resnet50": BackboneSpec(
         ctor=models.resnet50,
         weights_default=models.ResNet50_Weights.DEFAULT,