Each scenario resolves its project files from testdata/<TestName>/ by
convention: standalone compose files in their native format, directly
runnable with docker compose -f, copied to a temporary directory so the
committed files are never mutated. Subtests map to nested directories.
Ownership is strictly one test per directory: a check fails the suite on
any testdata directory no test owns, which is what keeps this from
degrading into a catch-all fixtures directory — no sharing, no
leftovers after a rename.
The inline Compose() declaration is removed; the demonstrator scenarios
move their models to testdata, including the multi-file build context
of TestUpBuildUnchangedContext (compose.yaml + Dockerfile + marker).
Signed-off-by: Nicolas De Loof <nicolas.deloof@gmail.com>
