test(conformance): add a sandbox smoke suite built on testkit

Add the `sandbox` crate to the conformance workspace with one testkit test that
creates a sandbox, runs `echo` in it with exec, deletes it and checks it is gone.
It is deliberately small: it exists so the runner can run a real test in a
tmachine environment on CI before the existing suites move to testkit.

The workspace's other crate, the CLI conformance suite, keeps running as it does
today. The conformance workspace joins the lockfile alignment check, so its
lockfile is realigned with the root lockfile.

The test is adapted from the `sandbox-lifecycle` suite in #4629.

Co-authored-by: Evan Lezar <elezar@nvidia.com>
Signed-off-by: Matthew Grossman <mgrossman@nvidia.com>

Author: matthewgrossman

tasks/scripts/check_cargo_lockfile_alignment.py

@@ -37,6 +37,7 @@
 # workspace here once its lockfile has been aligned with `--fix`.
 ALIGNED_WORKSPACES = (
     "tests/testkit",
+    "tests/suites/conformance",
 )