[AbuMareBear]

Adds assert_hash_attributes(hash, **expected), the hash counterpart to assert_attributes, extracted from Catberry's test helpers.

assert_hash_attributes(
  JSON.parse(response.body),
  "@type": "Person",
  name: "Marceline",
  nickname: nil
)

Changes

• Shared comparisons. The nil, Time, rich text, and assert_equal branches move into a private assert_value, used by both assertions. assert_attributes failure messages are unchanged.
• Key lookup. Each key is tried as given, then as a string, so symbol keys match parsed JSON. Catberry's version only looked up string keys.
• Missing keys fail with Expected hash to have key :nickname, but its keys were [...], even when the expected value is nil. Catberry's version treated a missing key as nil.
• RBS signatures, a README section, and a CHANGELOG entry.
• Metrics/ClassLength is excluded for tests, alongside the existing Metrics/AbcSize exclusion.

Testing

bundle exec rake: 27 runs, 0 failures; RuboCop clean. Every branch has a passing case and a failing case that checks the message, plus symbol vs. string keys and missing keys.