refactor: unsafe only in adapter + libkos; forbid(unsafe_code) everywhere else; libkos Window (volatile, bounds-checked MMIO/DMA/shared mem), entry!, thread::spawn; MapRegion returns pages; kernel const-built (with_cores/install_platform); newtype addrs

crates/kernel/src/syscall/mod.rs

@@ -96,7 +96,7 @@ impl<P: Platform> Kernel<P> {
             }
             Syscall::MapRegion { region, va, perms } => complete(
                 self.map_region_cap(pid, region, va, perms)
-                    .map(|()| SyscallResult::Ok),
+                    .map(|pages| SyscallResult::Value(pages.value() as usize)),
             ),
             Syscall::RegionAddress { region } => complete(
                 self.region_address_cap(pid, region)