Feature: Implement icebug-format spec

[aheev]

• Add our implementations for icebug-memory and icebug-disk specs in the repo
• Add converters to convert from formats like GraphAr to ladybugDB's icebug impl. Currently we can support the following
  • simple node tables with no indices and rel table with from, to cols to denote from and to nodes
  • GraphAr

[aheev]

completed via #506