hive_generator should complain about final fields

Just finished debugging to discover that a field was missing in the generated typeAdapter, because it was of type `final List`. hive_generator failed silently on this, generating code that wrote the field but didn't read it.

Even a simple warning could help here. All I needed to do to fix this was remove `final`.

Start at the hive_generator entry point that handles final fields and inspect the generated typeAdapter path for a final List. Reproduce the case and verify that generation no longer silently omits the read behavior, instead reporting the unsupported field clearly.

Written by the indexing model from the issue text.