CLI and vendoring tests

Test cases for the CLI and ESI vendoring surface (CLI and ESI vendoring (FEAT_0084)). Live under crates/ethercat-netcfg-cli/tests/.

Test Case: expand subcommand prints the build-equivalent module TEST_0841
status: open
verifies: REQ_0832

netcfg expand over a fixture prints to stdout a module byte-identical to the one the build helper writes to OUT_DIR for the same input.
Test Case: fetch vendors a remote ESI and records a pinned lockfile TEST_0842
status: open
verifies: REQ_0833, REQ_0835

Against a local HTTP test server, netcfg fetch downloads a referenced ESI into the vendored directory and writes a lockfile entry carrying the file’s content hash and the device revision. A second fetch with the server returning identical bytes is a no-op; a server returning altered bytes updates the recorded hash.
Test Case: Build fetches nothing; unvendored URL is a build error TEST_0843
status: open
verifies: REQ_0834

With network access denied to the build process, a fixture whose device references a web-URL ESI that has no vendored, pinned local copy fails the build with a “not vendored” error and makes no network request. The same fixture after netcfg fetch builds cleanly offline.