cmd/wol-proxy: add wol-proxy (#352)

add a wake-on-lan proxy for llama-swap. When the target llama-swap server is unreachable it will send hold a request, send a WoL packet and proxy the request when llama-swap is available.

cmd/wol-proxy/README.md

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+# wol-proxy
+
+wol-proxy automatically wakes up a suspended llama-swap server using Wake-on-LAN when requests are received.
+
+When a request arrives and llama-swap is unavailable, wol-proxy sends a WOL packet and holds the request until the server becomes available. If the server doesn't respond within the timeout period (default: 60 seconds), the request is dropped.
+
+This utility helps conserve energy by allowing GPU-heavy servers to remain suspended when idle, as they can consume hundreds of watts even when not actively processing requests.
+
+## Usage
+
+```shell
+# minimal
+$ ./wol-proxy -mac BA:DC:0F:FE:E0:00 -upstream http://192.168.1.13:8080
+
+# everything
+$ ./wol-proxy -mac BA:DC:0F:FE:E0:00 -upstream http://192.168.1.13:8080 \
+    # use debug log level
+    -log debug \
+    # altenerative listening port
+    -listen localhost:9999 \
+    # seconds to hold requests waiting for upstream to be ready
+    -timeout 30
+```
+
+## API
+
+`GET /status` - that's it. Everything else is proxied to the upstream server.