feat: implement configure_protection and map_shared with real page mapping, remove dead context_switch from Platform trait

crates/kernel/src/tests/mock_platform.rs

@@ -1,5 +1,4 @@
 use domain::memory::MemoryRegion;
-use domain::thread::SavedContext;
 use platform::Platform;
 use types::{
     address::{EntryPoint, PhysicalAddress, StackPointer},
@@ -31,7 +30,6 @@ impl MockPlatform {
 
 impl Platform for MockPlatform {
     fn configure_protection(&mut self, _process: ProcessId, _regions: &[MemoryRegion]) {}
-    fn context_switch(&mut self, _from: &mut SavedContext, _to: &SavedContext) {}
     fn enable_user_mode(&mut self, _entry: EntryPoint, _stack: StackPointer) -> ! {
         loop {}
     }