taktora backend snapshot tests

Live under crates/canopen-eds-codegen-taktora/tests/.

Test Case: EPOS4 backend output snapshot TEST_0630
status: open
verifies: REQ_0741, REQ_0742, REQ_0743, REQ_0744

Run parse → codegen → backend → prettyplease on the canonical EPOS4 EDS fixture. Compare the formatted output against a committed snapshots/epos4.rs golden file using insta::assert_snapshot!. Reviewer regenerates the golden when intentional changes land; CI fails on unintentional churn.
Test Case: Generated registry covers every emitted device TEST_0631
status: open
verifies: REQ_0745

For an input set with N EDS files, the generated module’s registry!() expansion contains exactly N entries mapping Identity → factory closure. White-box test parses the generated output and counts entries.
Test Case: Generated module compiles under no_std + alloc TEST_0632
status: open
verifies: REQ_0748

A test crate at crates/canopen-eds-codegen-taktora/tests/no_std_consumer/ has #![no_std] and extern crate alloc;, include!``s the generated module from a fixed input set, and compiles successfully. Catches any accidental ``std::-qualified path in the backend’s emit code.
Test Case: Backend is the sole canopen-eds-rt consumer in the toolchain TEST_0633
status: open
verifies: REQ_0740

CI shell check: cargo tree invocations for canopen-eds, canopen-eds-codegen, canopen-eds-build, canopen-eds-cli, and canopen-eds-verify must none of them list canopen-eds-rt in the dependency graph. canopen-eds-codegen-taktora is the only crate where canopen-eds-rt is allowed.
Test Case: Object-dictionary emission gated by feature flag TEST_0634
status: open
verifies: REQ_0747

Build the no_std_consumer test crate twice: once without features (the generated module exposes no OD symbol) and once with --features object-dictionary (the OD static exists with the expected entry count for the input set). Compares the two binaries’ rodata sections — the no-feature build is smaller by an amount approximating the OD table size.
Test Case: Dummy entries skipped in PDO struct fields TEST_0635
status: open
verifies: REQ_0744

Fixture EDS declares a PDO mapping containing one real 0x6040:00 entry, one Dummy32 entry, and one real 0x607A:00 entry. The generated PDO payload struct contains exactly two fields (the two real entries). The generated encode body writes zeros in the bit range covered by the dummy; the generated decode body skips it.
Test Case: Bring-up SDO writes emitted from EDS TEST_0636
status: open
verifies: REQ_0746

Snapshot test on the generated impl CanOpenConfigurable body for the EPOS4 fixture asserts the expected sequence of sdo.write(index, sub, value) calls: PDO comm params first, then PDO mapping params, then optional NMT start. Sequence and target indices match the EDS values exactly.