Update internal ASF Celix event loop to use libuv

[pnoltes]

Intro

This ticket focuses on the internal implementation changes related to Celix’s event loop and how libuv can be leveraged internally to simplify platform abstraction.

Ideally this can be done without breaking the public API.

Steps

• Replace internal event Loop with libuv event loop

Modify the internal Celix event thread implementation to use libuv's event loop (uv_loop_t). This will abstract the current Linux-specific implementation and make it cross-platform.

• Update the scheduled event implementation for libuv

Also update the scheduled event implementation to make use of libuv. Including usage of uv_timer_t if feasible.

• Update the celix shutdown procedure for the updated uv_loop_t

If feasible simplify the celix shutdown procedure using libuv.