Add MARC Authority to MADS 2.1 XML export

[dchud]

Add one-way export from MARC Authority records to MADS 2.1 XML, following the pattern established by the existing MODS conversion module.

Reference Specifications

• MADS home: https://www.loc.gov/standards/mads/
• MARC Authority to MADS 2.1 mapping (Excel): https://www.loc.gov/standards/mads/mads-mapping-2-1.xlsx
• XSLT 1.0 stylesheet: https://www.loc.gov/standards/marcxml/xslt/MARC21slim2MADS.xsl
• XSLT 2.0 stylesheet: https://www.loc.gov/standards/marcxml/xslt/MARC21slim2MADS_XSLT2.0.xsl
• MADS 2.1 schema (XSD): https://www.loc.gov/standards/mads/mads-2-1.xsd
• MARC Authority to MADS 2.0 mapping (HTML): https://www.loc.gov/standards/mads/mads-mapping.html

Scope

One-way conversion only: MARC Authority → MADS 2.1 XML. No reverse mapping (MADS → MARC Authority) — there is no official LOC crosswalk for that direction, and the LOC notes the forward mapping "is not intended to be a crosswalk that allows for bi-directional conversions without some loss of data."

Implementation Plan

1. Rust core module: src/mads.rs

Primary function:

pub fn authority_record_to_mads_xml(record: &AuthorityRecord) -> Result<String>

Also support converting a generic Record with leader/06=z:

pub fn record_to_mads_xml(record: &Record) -> Result<String>

Follow the manual XML construction pattern used in src/mods.rs (string building with std::fmt::Write), not the serde intermediate struct pattern.

2. Key field mappings (MARC Authority → MADS 2.1)

Authority headings (1XX → <mads:authority>):

• 100 → <mads:name type="personal">
• 110 → <mads:name type="corporate">
• 111 → <mads:name type="conference">
• 130 → <mads:titleInfo>
• 148 → <mads:temporal>
• 150 → <mads:topic>
• 151 → <mads:geographic>
• 155 → <mads:genre>

Variant headings (4XX → <mads:variant>):

• 400/410/411/430/448/450/451/455 → same descriptor types as above within <variant>

Related headings (5XX → <mads:related>):

• 500/510/511/530/548/550/551/555 → same descriptor types within <related>
• Map $w control subfield to type attribute (broader/narrower/earlier/later/equivalent)

Metadata elements:

• 008 positions → various attributes (e.g., encoding level)
• 010 → <mads:identifier type="lccn">
• 024 → <mads:identifier> with type from $2
• 040 → <mads:recordInfo> (cataloging source)
• 042 → <mads:recordInfo> (authentication code)
• 046 → date elements
• 370 → <mads:affiliation> or geographic metadata
• 371 → <mads:affiliation> (address)
• 372 → <mads:fieldOfActivity>
• 373 → <mads:affiliation> (group)
• 374 → <mads:occupation> or personInfo
• 375 → gender info
• 376 → <mads:familyInfo> or <mads:personInfo>
• 377 → <mads:language>
• 378 → <mads:name> (fuller form)
• 380-385 → various descriptive elements
• 667/670/675/678 → <mads:note>

Subdivision subfields ($v, $x, $y, $z in 1XX/4XX/5XX):

• $v → <mads:genre>, $x → <mads:topic>, $y → <mads:temporal>, $z → <mads:geographic>

3. PyO3 bindings

Add authority_record_to_mads() and record_to_mads() in src-python/src/formats.rs.

4. Python wrapper, type stubs, tests

• Expose in mrrc/__init__.py
• Add signatures to mrrc/_mrrc.pyi
• Rust unit tests + Python integration tests in tests/python/
• Validate output against the MADS 2.1 XSD schema

5. Documentation

• Update README.md format table (MADS row: Read=-, Write=Yes)
• Update docs/tutorials/rust/format-conversion.md — add MADS export example
• Update docs/tutorials/python/format-conversion.md — add MADS export example
• Update docs/reference/rust-api.md — document new public functions
• Update docs/reference/python-api.md — document new Python functions
• CHANGELOG entry

Design Notes

• MADS is to authority records what MODS is to bibliographic records; this feature complements existing MODS support
• The LOC XSLT stylesheets serve as an authoritative reference implementation for the mapping logic
• MADS 2.1 added new elements (personInfo, organizationInfo, familyInfo, fieldOfEndeavor, locale, workInfo) corresponding to MARC 37X fields

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Internal tracking: beads mrrc-b7l