perf(kernel): linked cap tree, translate-based page lookup, next-fit frames/heap, targeted dequeue; host benches

crates/platform/src/lib.rs

@@ -50,6 +50,10 @@ pub trait Platform {
     ) -> Result<(), MapError>;
     /// Removes the mapping at `va` and flushes it from the TLB.
     fn unmap_page(&mut self, process: ProcessId, va: VirtualAddress);
+    /// The frame `va` is mapped to in `process`, if any. Only a lookup:
+    /// the kernel confirms every answer against its own frame table, so a
+    /// wrong answer can make the kernel refuse but never trust a frame.
+    fn translate(&self, process: ProcessId, va: VirtualAddress) -> Option<PhysicalAddress>;
     /// Fills a frame with zeros before it is handed to a process.
     fn zero_frame(&mut self, pa: PhysicalAddress);