feat: create libkos crate with core modules (syscall, alloc, rt)

crates/libkos/src/arch/mod.rs

@@ -0,0 +1,9 @@
+#[cfg(all(target_arch = "riscv64", target_os = "none"))]
+mod riscv;
+#[cfg(all(target_arch = "riscv64", target_os = "none"))]
+pub use riscv::*;
+
+#[cfg(not(target_os = "none"))]
+mod mock;
+#[cfg(not(target_os = "none"))]
+pub use mock::*;