Add Nix flake for mciasctl and mciasgrpcctl

Vendor dependencies and expose control program binaries via
nix build. Uses nixpkgs-unstable for Go 1.26 support.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/github.com/google/uuid/doc.go

@@ -0,0 +1,12 @@
+// Copyright 2016 Google Inc.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package uuid generates and inspects UUIDs.
+//
+// UUIDs are based on RFC 4122 and DCE 1.1: Authentication and Security
+// Services.
+//
+// A UUID is a 16 byte (128 bit) array.  UUIDs may be used as keys to
+// maps or compared directly.
+package uuid