BazaRb#push leaks NoMethodError for non-String data

[gemshrine]

Symptom and impact

BazaRb#push documents data as a String, but it does not validate that type before calling String-only methods. Passing a different value raises a raw NoMethodError instead of the client's normal argument-validation error. The fake client has the same gap, so tests can fail with a different low-level exception rather than a clear input error.

Steps to reproduce

client = BazaRb.new('example.org', 443, 'token')
client.push('valid-job', 42, [])

The call fails before making an HTTP request: push reaches data.empty? with an Integer. The same input to BazaRb::Fake.new.push('valid-job', 42, []) also reaches data.empty? without a type check.

Actual result

Both clients leak NoMethodError for Integer#empty?. Callers do not get an error identifying data as the invalid argument.

Expected result

The real and fake clients should reject non-String data with a clear validation error before starting upload work, consistent with the documented String parameter and the validation of nil and empty data.

Technical evidence

lib/baza-rb.rb checks only nil and emptiness for data before passing it to File.binwrite; lib/baza-rb/fake.rb performs the same nil and emptiness checks. Neither path verifies data.is_a?(String). Existing tests cover nil and empty data but not other types.