[PJK]

Summary

• Adds cbor_map_get(const cbor_item_t *map, const cbor_item_t *key, bool (*eq)(const cbor_item_t *, const cbor_item_t *)) to maps.h/maps.c
• 11 tests in test/map_get_test.c
• Documentation in doc/source/api/type_5_maps.rst
• Changelog entry

Design rationale

The equality function is parameterized on purpose. The two main reasons:

1. Type-specific comparators are cheaper. Most protocols constrain map keys to a single type (e.g., WebAuthn/COSE use small integers; JSON-derived formats use text strings). A comparator that only handles one type avoids the full dispatch overhead of a generic comparator and can be inlined by the compiler.

2. Any data-model semantics can be plugged in. Callers can pass cbor_structurally_equal for exact encoding-level matching, a width-ignoring integer comparator, a case-insensitive string comparator, or anything else — without the library needing to anticipate every use case.

Usage

// Structural equality (encoding-level): uint8(1) ≠ uint16(1)
cbor_item_t *v = cbor_map_get(map, key, cbor_structurally_equal);

// Custom comparator that ignores integer encoding width
cbor_item_t *v = cbor_map_get(map, key, my_int_value_eq);

The returned item has its reference count incremented; caller must cbor_decref it. Returns NULL if no key matched.

Closes #96 (alongside #408).

Test plan

• ctest -R map_get_test passes (11/11)
• bash clang-format.sh produces no diff
• CI green

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.59%. Comparing base (dd5676a) to head (31b52ef).
⚠️ Report is 14 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #409      +/-   ##
==========================================
+ Coverage   99.53%   99.59%   +0.05%     
==========================================
  Files          20       20              
  Lines        1731     1737       +6     
==========================================
+ Hits         1723     1730       +7     
+ Misses          8        7       -1     

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