[Ruby] Release 0.58.0

Performance

• oneOf and anyOf whose branches each require a property fixed to a distinct string validate only the branch matching the instance's value.
• Meta.valid? and Meta.validate! check a schema against the bundled drafts without converting it first, 2 to 5x faster on the benchmarked schemas.

Fixed

• Canonical.find_unsatisfiable missing a oneOf over $ref branches beside a sibling none of them admits.
• A value with no JSON form nested under type: null failing validation silently (it should raise TypeError).