The serde traits are now directly implemented for FieldMask - this helps address potential serde issues with wrapper types, and simplifies the serde process somewhat.
If using #[serde(with = ...)] with an Option type, serde will expect all marked fields to be present. Adding #[serde(default)] restores expected behaviour - if no Option value is present, None will be used.
This is an incremental change towards a strongly-typed util module,
aimed at reducing dependency on the DictObject class. The rough idea is
to annotate everything as Dict, add some tests to codify the existing
behavior, and then start defining dataclasses for the dischovery schema.
We also remove some unused logic & params.
Make a few changes in the toplevel src dir to help separate
templates from code. Specifically, we rename `src/mako` to
`src/generator`, and nest the mako templates inside a
`src/generator/templates` dir.
This isolates most Python code into the `src/generator/lib` dir.
