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/go-tpm/tpm2/kdf.go

@@ -0,0 +1,29 @@
+package tpm2
+
+import (
+	"crypto"
+
+	legacy "github.com/google/go-tpm/legacy/tpm2"
+)
+
+// KDFa implements TPM 2.0's default key derivation function, as defined in
+// section 11.4.9.2 of the TPM revision 2 specification part 1.
+// See: https://trustedcomputinggroup.org/resource/tpm-library-specification/
+// The key & label parameters must not be zero length.
+// The label parameter is a non-null-terminated string.
+// The contextU & contextV parameters are optional.
+func KDFa(h crypto.Hash, key []byte, label string, contextU, contextV []byte, bits int) []byte {
+	return legacy.KDFaHash(h, key, label, contextU, contextV, bits)
+}
+
+// KDFe implements TPM 2.0's ECDH key derivation function, as defined in
+// section 11.4.9.3 of the TPM revision 2 specification part 1.
+// See: https://trustedcomputinggroup.org/resource/tpm-library-specification/
+// The z parameter is the x coordinate of one party's private ECC key multiplied
+// by the other party's public ECC point.
+// The use parameter is a non-null-terminated string.
+// The partyUInfo and partyVInfo are the x coordinates of the initiator's and
+// the responder's ECC points, respectively.
+func KDFe(h crypto.Hash, z []byte, use string, partyUInfo, partyVInfo []byte, bits int) []byte {
+	return legacy.KDFeHash(h, z, use, partyUInfo, partyVInfo, bits)
+}