Fix build action

[Uacias]

Currently our build gh action is failing with this error:

error[E0425]: cannot find function `run_generated_state_machines` in this scope
   --> proxy/src/core/utils.rs:155:13
    |
155 |             run_generated_state_machines(request_body, response_body, path.to_string());
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not found in this scope

For more information about this error, try `rustc --explain E0425`.
warning: `proxy` (bin "proxy") generated 1 warning
error: could not compile `proxy` (bin "proxy") due to 1 previous error; 1 warning emitted
warning: build failed, waiting for other jobs to finish...

This is possibly due to using build.rs, needs further investigation, to keep the codebase clean and make sure build always passes.