refactor(adapter): split trap/page_table/smp/entry by concern; trim comments

crates/adapter-riscv/src/platform.rs

@@ -64,9 +64,8 @@ impl Platform for RiscVPlatform {
         let Some(root) = self.root(process) else {
             return;
         };
-        // No hart may still translate through it once the kernel frees its
-        // frames: other harts leave it (and wait for nothing but that), and
-        // the caller may be tearing down the space we are running on.
+        // No hart may translate through it once its frames are freed; that
+        // includes this one, which may be running on it.
         smp::shoot_down(root);
         if mmu::active_root() == root {
             // SAFETY: the kernel page table lives in the boot heap forever.