Scan all enum definitions in api.proto at codegen time and automatically
populate max_value for enum-typed fields. This eliminates the need for
manual (max_value) annotations on every enum field.
When max_value < 128, the generated calculate_size uses constant-size
arithmetic instead of a function call:
- `calc_uint32(1, static_cast<uint32_t>(field))` → `field ? 2 : 0`
For repeated enum fields with constant element size, the per-element
loop is replaced with a multiply: `size += count * bytes_per_element`.
J. Nick Koston
37258de6b1