Move code mode tool files under tools/code_mode and split functionality

[pakrym-oai]

• Summary
  • migrate the code mode handler, service, worker, process, runner, and bridge assets into the tools/code_mode module tree
  • split Execution, protocol, and handler logic into dedicated files and relocate the tool definition into code_mode/spec.rs
  • update core references and tests to stitch the new organization together
• Testing
  • Not run (not requested)

[cconger]

Thank you!