Add branded types for RDF namespace and prefix identifiers

[kmcginnes]

Description

• Add types.ts with IriNamespace, IriLocalValue, IriParts, RdfPrefix, GeneratedPrefix, and NormalizedIriNamespace branded types
• Apply branded types to PrefixTypeConfig (prefix and uri fields)
• Add branded type casts to existing logic and test files
• Update steering docs with branded type table entries and backward compatibility testing guidance

Validation

• pnpm check:types passes with no errors
• pnpm test passes with no failures
• Existing behavior is unchanged; only type-level safety is added

Related Issues

• Part of SPARQL namespaces seem to be reused #258

Check List

• I confirm that my contribution is made under the terms of the Apache 2.0
  license.
• I have run pnpm checks to ensure code compiles and meets standards.
• I have run pnpm test to check if all tests are passing.
• I have covered new added functionality with unit tests if necessary.
• I have added an entry in the Changelog.md.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.23%. Comparing base (c5affc5) to head (673240b).
⚠️ Report is 74 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1538       +/-   ##
===========================================
+ Coverage   47.81%   65.23%   +17.42%     
===========================================
  Files         382      355       -27     
  Lines        8525     7930      -595     
  Branches     3159     2901      -258     
===========================================
+ Hits         4076     5173     +1097     
+ Misses       3070     1990     -1080     
+ Partials     1379      767      -612     

Flag	Coverage Δ
unittests	65.23% <100.00%> (+17.42%)	⬆️

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