fix: sched round-robin, cap slot OOB panic, clippy, make ci

- RunList -> intrusive FIFO, no starvation, no silent drop
- cap table sized to CapSlot range (kani caught OOB panic)
- snake food color test uses const
- kani cfg lint, RUST_MIN_STACK for big kernel struct in tests

crates/elf/src/lib.rs

@@ -134,7 +134,7 @@ impl ElfInfo {
     pub fn total_pages(&self) -> usize {
         let mut total = 0;
         for seg in self.segments() {
-            total += (seg.mem_size + 4095) / 4096;
+            total += seg.mem_size.div_ceil(4096);
         }
         total
     }