Generate RevBuilder structs in codegen alongside ProtoBuilder.
RevBuilder writes fields into a buffer starting from the end,
allowing fields to be set in reverse declaration order. This
avoids reallocation and produces valid protobuf data matching
the forward layout.
Update generated interop files and add comprehensive tests for
wire format, nesting, map entries, overflow handling, and buffer
marking utilities.
Add #![no_std] to the runtime crate and introduce optional std and
alloc features. Update the code generator to be compatible and add a
no_std_test example. Remove the generator binary.
Update the generator to detect map fields and use MapFieldIterator.
Implement MapFieldIterator in the runtime to handle key-value pair
extraction and add write_map_entry to ProtoBuilder. Add tests to
verify that map-bearing messages generate and compile correctly.
charles