Network-config parser and IR

Parser crate requirements for Network-config parser and IR (FEAT_0081) — reading network.yaml into a typed IR that is independent of code emission.

Feature: Network-config parser and IR FEAT_0081
status: open
satisfies: FEAT_0080
is satisfied by: REQ_0820, REQ_0821, REQ_0822, REQ_0823, REQ_0824
is refined by: ADR_0096

A parser crate. Reads network.yaml, emits a typed in-memory IR (the “Device / SubDevice” data model). Knows nothing about code emission. Suitable for any downstream tool — codegen, a topology visualiser, a validator.
Requirement: YAML parse to typed network IR REQ_0820
status: open
satisfies: FEAT_0081
is verified by: TEST_0830

The crate shall expose a parse entry point that deserialises a network.yaml document into a typed NetworkConfig IR via serde. Parsing the YAML text itself shall perform no code emission; resolution of referenced ESI files is the parser’s only filesystem access.
Requirement: IR carries bus config, device instances, and channel bindings REQ_0821
status: open
satisfies: FEAT_0081
is verified by: TEST_0830

The IR shall represent: a BusConfig (cycle time, distributed-clocks flag, max_subdevices / max_pdi_bytes compile-time bounds, optional default NIC); a Vec<DeviceInstance> in bus order, each carrying a label, a DeviceSource (Esi { path, pinned_hash, revision } or Inline { rx, tx }), an optional Identity, an optional station_alias, and an optional address override; and a Vec<ChannelBinding> carrying channel name, device label, direction, bit offset, bit length, element type, and an allow_overlap flag.
Requirement: One file describes exactly one bus REQ_0822
status: open
satisfies: FEAT_0081
is verified by: TEST_0831

One network.yaml document shall describe exactly one EtherCAT bus — one connector, one NIC, one process image. Multi-bus documents shall be rejected by the parser. Multiple buses are expressed as multiple files producing multiple generated modules (see One file, one bus; multi-bu... (ADR_0096)).
Requirement: Devices referenced by stable label, not address REQ_0823
status: open
satisfies: FEAT_0081
is verified by: TEST_0832

Each device instance shall carry a stable string label. Channel bindings shall reference their device by label, never by raw configured address or list index, so that the configured address (assigned per Emit static SubDeviceMap PD... (REQ_0825)) remains a derived value and reordering devices does not require editing channel bindings.
Requirement: Parser depends on ethercat-esi, never on the connector runtime REQ_0824
status: open
satisfies: FEAT_0081
is verified by: TEST_0833

The ethercat-netcfg crate shall depend on ethercat-esi and fieldbus-od-core (to resolve ESI references and validate inline offsets against a device’s real PDO layout) and shall not declare taktora-connector-ethercat as a dependency.