BC and general reworking for handling `uv_spawn` for child subprocess calling

This version onward will use uv_spawn and other features of libuv for subprocess execution, if not install the fallback will use previous system of proc_open.

• update namespaces
• update Parallel success, fail, and timeout call signature, added signal handling
• update Parallel to require Coroutine class at creation, increase concurrency
• update required and readme/docs references
• remove sub process default timeout
• moved constants/stubs to symplely/spawn
• Use Github Actions for all CI builds/tests