ObjectCodec implementations should be tested with legacy files (to ensure that we don't break old files without noticing)

[rcaudy]

A number of our ObjectCodec implementations are not currently used by default (for example, BigDecimalCodec). We typically have round-trip tests, verifying that they can still write and re-read data correctly. We should also have Parquet-based tests wherein we verify that we can still consume old files correctly, in order to catch cases when we inadvertently change the interpretation of previously-written data and prevent us from breaking support for user files.