Union tags are cast unchecked

[ghost]

Union tags are cast from i64 to usize when decoding without checking that the conversion makes sense. This has weird effects, such as on 32 bit platforms interpreting the tag 4294967300 as a 4. https://github.com/flavray/avro-rs/blob/7b820c13a1f25c7fd35850a6fed921aabc3ed103/src/decode.rs#L124

[martin-g]

This is fixed with

1. https://github.com/flavray/avro-rs/commit/d719de228131a8978e230f8b404c5bf07ef89567
2. https://github.com/flavray/avro-rs/commit/b3edfacced605a9d3229426441a2808176c86120#diff-aeece9508d349335fdebc30632ef26fa2851aa73336dea735c78d36cb7e77b2b