Substitute libco for libmicrokitco to perform blocking I/O in Micropython

[dreamliner787-9]

This pull request:

• Remove lib/libco
• Changes Micropython's blocking implementation from using libco to libmicrokitco:
  • Up to 62 (MICROKIT_MAX_CHANNELS) event sources are now possible. We are no longer limited by the 32-bits int bitfield, consequently, the event source abstraction is no longer needed.
  • Cothreads can now return normally instead of having to explicitly yield the control to another cothread.
  • The underlying libco primitives' memory layout has been updated. The registers region now comes after the stack top. If Micropython or other clients using libmicrokitco overflow the stack, it won't overwrite the registers region.

[JE-Archer]

If you are adding a dependency on libmicrokitco and libmicrokitco contains a copy of libco, why update the libco in the Lions OS repository instead of just removing it?

[dreamliner787-9]

If you are adding a dependency on libmicrokitco and libmicrokitco contains a copy of libco, why update the libco in the Lions OS repository instead of just removing it?

Just in case someone still need it, but I'm happy to remove it.

[Ivan-Velickovic]

lionsos/libco should be removed. Whether libmicrokitco lives in Microkit, LionsOS, or as its own repo we can discuss later.

Before reviewing this PR I'll first look at design/code for libmicrokitco in more detail.