* Refactor idl_gen_rust to a ForAllX continuation pattern.
* Removed unneeded SetValue and updated sample rust gencode
* Make Rust flatbuffers print right
* Generated code and removed unnecessary trait constraint
* bumped rust version. Release required
* removed an unwrap in Rust Debug-print unions
* Tested formatting flatbuffers in rust.
* Set float precision in flaky debug-print test
* impl Debug for structs too
Co-authored-by: Casper Neo <cneo@google.com>