WiP: Migrating to Alpine build env

[Ralim]

Ticking off a long term goal of (a) getting off the nuclei compiler to a standard riscv one and (b) faster CI times.

What this does:

1. Swaps out Ubuntu for Alpine Linux
2. Swaps out the Nuclei compiler for the standard ones packaged by Alpine
3. -> Bit of a hack required as the riscv compiler doesnt package m_nano (nano math lib)

The standard riscv compiler produces slightly larger code than the nuclei one (<1%) so dont really care at this point, given the gain of using a standard compiler.

To do still:

• Retest all firmware builds
• Cleanup Makefile