"sinceVersion" is not checked against schema version during code generation

[entangled90]

When adding a new field it's usually added with a sinceVersion attribute, but it may happen by error that the version of the schema is not bumped.
This leads to issues when decoding the field as the field is encoded correctly and is decoded correctly using OTF decoder (it probably skip sinceVersion checks?)
However the generated Java decoders skip this field as it was encoded with a previous version.

I suggest to check during code generation to check if the field version is strictly greater than the schema version as it's probably a bug.

I propose to just fail code generation if this situation occurs so that the schema version can be bumped manually.

If you can point me where it's best to implement this check I can create a pull request myself.

Hope this helps, thank you for all the work!