SDK Versioning Improvements (#77)

* Add SDK_BRANCH

start_server.sh

@@ -47,20 +47,32 @@ JSON
 }
 
 function install_vastai_sdk() {
+    # If SDK_BRANCH is set, install vastai-sdk from the vast-sdk repo at that branch/tag/commit.
+    if [ -n "${SDK_BRANCH:-}" ]; then
+        if [ -n "${SDK_VERSION:-}" ]; then
+            echo "WARNING: Both SDK_BRANCH and SDK_VERSION are set; using SDK_BRANCH=${SDK_BRANCH}"
+        fi
+        echo "Installing vastai-sdk from https://github.com/vast-ai/vast-sdk/ @ ${SDK_BRANCH}"
+        if ! uv pip install "vastai-sdk @ git+https://github.com/vast-ai/vast-sdk.git@${SDK_BRANCH}"; then
+            report_error_and_exit "Failed to install vastai-sdk from vast-ai/vast-sdk@${SDK_BRANCH}"
+        fi
+        return 0
+    fi
+
     if [ -n "${SDK_VERSION:-}" ]; then
         echo "Installing vastai-sdk version ${SDK_VERSION}"
         if ! uv pip install "vastai-sdk==${SDK_VERSION}"; then
             report_error_and_exit "Failed to install vastai-sdk==${SDK_VERSION}"
         fi
-    else
+        return 0
+    fi
+
     echo "Installing default vastai-sdk"
     if ! uv pip install vastai-sdk; then
         report_error_and_exit "Failed to install vastai-sdk"
     fi
-    fi
 }
 
-
 [ -n "$BACKEND" ] && [ -z "$HF_TOKEN" ] && report_error_and_exit "HF_TOKEN must be set when BACKEND is set!"
 [ -z "$CONTAINER_ID" ] && report_error_and_exit "CONTAINER_ID must be set!"
 [ "$BACKEND" = "comfyui" ] && [ -z "$COMFY_MODEL" ] && report_error_and_exit "For comfyui backends, COMFY_MODEL must be set!"