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/legacy/tpm2/README.md

@@ -0,0 +1,35 @@
+# TPM 2.0 client library
+
+## Tests
+
+This library contains unit tests in `github.com/google/go-tpm/tpm2`, which just
+tests that various encoding and error checking functions work correctly. It also
+contains more comprehensive integration tests in
+`github.com/google/go-tpm/tpm2/test`, which run actual commands on a TPM.
+
+By default, these integration tests are run against the
+[`go-tpm-tools`](https://github.com/google/go-tpm-tools)
+simulator, which is baesed on the
+[Microsoft Reference TPM2 code](https://github.com/microsoft/ms-tpm-20-ref). To
+run both the unit and integration tests, run (in this directory)
+```bash
+go test . ./test
+```
+
+These integration tests can also be run against a real TPM device. This is
+slightly more complex as the tests often need to be built as a normal user and
+then executed as root. For example,
+```bash
+# Build the test binary without running it
+go test -c github.com/google/go-tpm/tpm2/test
+# Execute the test binary as root
+sudo ./test.test --tpm-path=/dev/tpmrm0
+```
+On Linux, The `--tpm-path` causes the integration tests to be run against a
+real TPM located at that path (usually `/dev/tpmrm0` or `/dev/tpm0`). On Windows, the story is similar, execept that
+the `--use-tbs` flag is used instead.
+
+Tip: if your TPM host is remote and you don't want to install Go on it, this
+same two-step process can be used. The test binary can be copied to a remote
+host and run without extra installation (as the test binary has very few
+*runtime* dependancies).