[Rust] lib.rs will be generated with "#![forbid(unsafe_code)]"

Author: Michael Ward

sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/rust/LibRsDef.java

@@ -76,6 +76,7 @@ void generate() throws IOException
  {
  try (Writer libRs = outputManager.createOutput("lib"))
  {
+ indent(libRs, 0, "#![forbid(unsafe_code)]\n");
  indent(libRs, 0, "#![allow(clippy::upper_case_acronyms)]\n");
  indent(libRs, 0, "#![allow(non_camel_case_types)]\n");
  indent(libRs, 0, "use core::{convert::TryInto};\n\n");