Bump default stack size for target pico to 8kb from 2kb

targets/pico.json

@@ -4,6 +4,7 @@
     ],
     "build-tags": ["pico"],
     "serial-port": ["2e8a:000A"],
+    "default-stack-size": 8192,
     "ldflags": [
         "--defsym=__flash_size=2048K"
     ],