Add a scheduler which just keeps of processes for now, and a

with_process to interact with them. User space now has it's own address
space and mapper which means we will be able to allocate memory for it.
I added a bunch of functions as stubs into libxunil which are required
for doomgeneric.

user/libxunil/rust-toolchain.toml

@@ -0,0 +1,8 @@
+[toolchain]
+channel = "nightly"
+targets = [
+    "x86_64-unknown-none",
+    # "aarch64-unknown-none",
+    # "riscv64gc-unknown-none-elf",
+    # "loongarch64-unknown-none",
+]