feat: Spinner should keep spinning while process is running

[tkolleh]

Summary

This PR transitions the roda.lua library from a synchronous, blocking architecture to a fully asynchronous, non-blocking architecture using luv (libuv bindings for Lua). This ensures that the terminal spinner animates smoothly in the background while child processes execute, without freezing the Lua runtime.

Key Changes

• Asynchronous Timers: Replaced manual system.gettime() checks and blocking while loops with uv.new_timer(). The spinner now renders frames automatically in the background event loop.
• Non-Blocking Child Processes: Implemented Spinner:execute(command, args) using uv.spawn. This allows child processes to run concurrently without halting the main Lua thread.
• Async Stream Handling: Standard output (stdout) from child processes is now captured asynchronously via uv.read_start(), preventing memory overflow and blocking during long-running commands.
• Functional Bracket Pattern: Introduced a reusable async_bracket utility (Continuation-Passing Style) in roda.util. This guarantees safe acquisition and release of libuv resources (timers, pipes, process handles), preventing memory leaks even if errors occur.
• Event Loop Integration: Added roda.run() to expose the libuv event loop, allowing the script to wait for all asynchronous tasks to complete.

Benefits

• Smooth Animations: The spinner no longer stutters or stops when waiting for a process to finish.
• Performance: Multi-platform asynchronous I/O natively supported by libuv (epoll, kqueue, IOCP).
• Robustness: The functional bracket pattern ensures that all C-level resources are safely closed, eliminating potential memory leaks.
• Composability: The Continuation-Passing Style (CPS) API sets the foundation for future functional enhancements like Promises or Task monads.