Freeze the Go implementation as a test-only oracle, with vectors

oracle/go is the Go code at 4c1507c, moved unchanged, plus test-only
generators that record what it computes. tests/vectors holds the
deterministic crypto/store vectors and synthetic fixtures they produce.

Co-Authored-By: Claude <noreply@anthropic.com>

oracle/go/agent_linux.go

@@ -0,0 +1,11 @@
+// Copyright 2026 The vault Authors.
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package main
+
+import "golang.org/x/sys/unix"
+
+// Not dumpable also means not ptrace-able by the same user.
+func init() {
+	undumpable = func() { unix.Prctl(unix.PR_SET_DUMPABLE, 0, 0, 0, 0) }
+}