refactor: run cores and builds in a sandbox

core_probe starts its worker with only the --env values, the worker clears its own environment before loading the core, and a working bubblewrap runs it with a read-only tree, no network and the user's credentials masked. The record names the isolation used. A timeout kills the whole process group. campaign.py starts core_probe, git, make and romfetch with the allowlist, make inside the same sandbox. --record refuses a folder that is not a checkout root.

schemas/core-probe-record.schema.json

@@ -686,6 +686,10 @@
         "tracing": {
           "type": "string"
         },
+        "isolation": {
+          "type": "string",
+          "description": "How the core ran: `bwrap` (read-only tree, no network, the user's credentials masked, an empty environment beside the --env values) or `environment only: ...` with the reason bubblewrap was not used."
+        },
         "input_queries": {
           "type": "integer",
           "minimum": 0