Refactor request generators to populate a script.RequestData intermediate struct, then apply it to fasthttp.Request in one step. This eliminates the round-trip conversion (fasthttp → RequestData → fasthttp) when scripts are enabled. Remove the URL field from RequestData and the now-unused fasthttp conversion functions from chain.go.
Replace ad-hoc fmt.Errorf/errors.New calls with typed error structs across config, sarin, and script packages to enable type-based error handling. Add script-specific error handlers in CLI entry point. Fix variable shadowing bug in Worker for scriptTransformer. Bump Go to 1.25.7 and golangci-lint to v2.8.0.
- Add FileCache for caching local files and remote URLs in memory
- Update body_FormData to accept variadic key-value pairs with file support
- Use @ prefix for file paths (local or HTTP/HTTPS URLs)
- Use @@ to escape literal @ values
- Add file_Base64 function for Base64 encoding files
- Update documentation with new syntax and examples
