IDS 1.0 writer and producer constructors (0.1.4)

[GeneralPawz]

Closes #10.

What

• to_string / to_writer write the typed model as IDS 1.0: IDS/xs/xsi namespaces and the 1.0 xsi:schemaLocation, XSD element order, simpleValue vs xs:restriction as the Value holds them, @cardinality on every requirement facet, optional elements omitted when None.
• Refusals with a typed WriteError + model path (e.g. specifications[0]/requirements/facets[2]/@dataType): non-1.0/conflicting version, no specifications, no IFC release, empty or out-of-order applicability, xs:restriction without facets or with unknown base, non-required entity requirement, optional partOf, @uri where not allowed, invalid dataType/author/date, characters XML 1.0 cannot carry. to_writer writes nothing for a refused model.
• Producer constructors: Ids::new (declares 1.0, no fake Detected evidence), Info::new, Specification::new (optional applicability) + require, Applicability::set_occurrence, Requirement::new/with_occurrence, facet news, Restriction::enumeration/pattern, From into Value/Facet/Requirement.
• Version 0.1.4 (additive API).

Evidence

$ ./scripts/gate.sh                     # exit 0
$ IDS_TEST_CASES=… cargo test --test corpus -- --ignored
test corpus_every_case_reads_as_declared_ids_1_0 ... ok
test corpus_every_case_round_trips_through_the_writer ... ok      # 334 cases, read(write(read(x))) == read(x), fixed point
test written_documents_validate_against_the_official_xsd ... ok  # 334 + kitchen sink via xmlschema; negative control rejected

The XSD is not vendored; scripts/validate-ids.py reads it from the local buildingSMART checkout. Mutations (unescaped \n/\r, dropped optional cardinality, dropped minOccurs) are each caught — see PLAN.md.

https://claude.ai/code/session_01DiS9fZk8w57TKopxGHYYaK