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/google.golang.org/protobuf/internal/genid/goname.go

@@ -0,0 +1,20 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package genid
+
+// Go names of implementation-specific struct fields in generated messages.
+const (
+	State_goname = "state"
+
+	SizeCache_goname  = "sizeCache"
+	SizeCacheA_goname = "XXX_sizecache"
+
+	UnknownFields_goname  = "unknownFields"
+	UnknownFieldsA_goname = "XXX_unrecognized"
+
+	ExtensionFields_goname  = "extensionFields"
+	ExtensionFieldsA_goname = "XXX_InternalExtensions"
+	ExtensionFieldsB_goname = "XXX_extensions"
+)