Correct module paths and accessor usage in the generator to ensure
generated code builds. Add a test that verifies this by compiling the
generated code in a temporary project.
Use absolute paths for temporary project directories and dependencies
to improve reliability. Update the generated Cargo.toml with additional
dependencies and remove the offline flag from cargo build.
Generate `which_<oneof>` methods and corresponding enums to handle
oneof fields in generated messages. Also add `has_<field>` helper
methods for all fields.
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