flagging columns null instead of null from table config

currently enabled null support is a table-level configuration. we need to create column-level null support to indicate whether a column is nullable.

This:
1. enables calcite to generate more efficient plan when column is non-nullable.
2. provide runtime better boxing/unboxing optimization, currently everything need to handle in generic fashion

The issue does not name files, tests, or entry points. Start by locating the table-level null-support configuration and tracing how Calcite planning and runtime boxing/unboxing consume it; done means nullability can be specified per column and both planning and runtime handling use that information.

Written by the indexing model from the issue text.