Parser and IR tests

Test cases for the parser crate (Network-config parser and IR (FEAT_0081)). Per-crate, no I/O beyond test fixtures, parallel-safe. Live under crates/ethercat-netcfg/tests/.

Test Case: parse() accepts a representative WAGO network.yaml TEST_0830
status: open
verifies: REQ_0820, REQ_0821

Loads a canonical network.yaml fixture describing a WAGO 750-354 coupler with two channels, calls the parse entry point, and asserts the resulting NetworkConfig carries the expected BusConfig (cycle time, max_subdevices / max_pdi_bytes), one DeviceInstance with its label and DeviceSource, and two ChannelBinding entries with the expected direction, bit offset, and bit length.
Test Case: Multi-bus document is rejected TEST_0831
status: open
verifies: REQ_0822

A fixture declaring two top-level buses in one document parses to an error naming the one-file-one-bus rule. A single-bus fixture parses without error. Guards the scope boundary of One file, one bus; multi-bu... (ADR_0096).
Test Case: Channels resolve to devices by label, stable under reorder TEST_0832
status: open
verifies: REQ_0823

A fixture whose channels reference devices by label parses correctly; reordering the device list in the fixture (without editing any channel) leaves every channel bound to the same device. Confirms bindings key on label, not list index or address.
Test Case: Parser is independent of the connector runtime TEST_0833
status: open
verifies: REQ_0824

cargo tree -p ethercat-netcfg shall not list taktora-connector-ethercat anywhere in the resolved graph. Implemented as a CI shell check that greps the output and fails on match. ethercat-esi and fieldbus-od-core are expected present.