test: assert four leaf-crate smoke tests, and two more census fixes

Two more census heuristics, both verified by bisecting the candidate count so a "fix" that widened the queue could not slip through:

- any `assert*!` macro counts as verification, not just the three built-ins — `assert_fields_bound!` in `protos` was being missed. The pattern deliberately stays a substring match: an earlier attempt anchored it with `\b`, which silently stopped matching prefixed macros like `const_assert!` and pushed the queue from 32 to 55 before the count caught it.
- `let _ = Type::<T>::method;` is a signature guard, the same as the already-recognised nested-fn form. That is `iam`'s deprecated-API test.

Tree-wide candidates go 32 to 30 from the script alone, then to 26 with the four tests below.

`detect_storage_media`'s two tests only checked that the call did not panic, over a `match` whose arms were all empty. What the machine reports depends on the machine, but two rules do not: an override wins over probing, including when probing is disabled, and disabled probing reports `Unknown` rather than guessing. A third test keeps the platform call and asserts it returns a known variant *and* the same one twice — a probe that flapped would make the scheduler's profile depend on when it asked.

`runtime_facade_stops_empty_replay_workers` called the stop path and asserted nothing. It now checks the worker list is empty afterwards and that a second call stays harmless, which is what shutdown paths actually do.

`test_mask_never_recurses_for_any_variant` discarded every mask. Termination is still the property under test — a regression overflows the stack rather than failing an assertion — but the masks are now collected and checked, so the loop cannot fold away and a variant that starts returning an empty mask is caught too.

Two known false positives are left in the queue rather than chased: `utils/src/string.rs:942` does assert, but its input string `"{1...2}}"` unbalances the scanner's brace counter and truncates the body before the assertion. Making the counter literal-aware needs a lexer that understands raw strings — a first attempt desynchronised on `r#"{"invalid": json}"#` and pushed the queue to 120, so it was backed out. `s3select-api:379` declares a nested exhaustive-match fn and never calls it; recognising that shape without hiding genuinely empty bodies needs more care than it is worth today.

Refs backlog#1836

crates/notify/src/runtime_facade.rs

@@ -527,9 +527,19 @@ mod tests {
     }
 
     #[tokio::test]
-    async fn runtime_facade_stops_empty_replay_workers() {
+    async fn stopping_replay_workers_is_a_no_op_when_there_are_none() {
         let (facade, _, _) = build_facade();
+
         facade.stop_replay_workers().await;
+
+        // The stop path takes the worker list and hands it to the adapter, so an
+        // empty facade must come back with the list still empty and dispatch
+        // released rather than left paused (rustfs/backlog#1836).
+        assert!(facade.replay_workers.read().await.is_empty());
+
+        // Calling it twice must stay harmless: shutdown paths do exactly that.
+        facade.stop_replay_workers().await;
+        assert!(facade.replay_workers.read().await.is_empty());
     }
 
     #[tokio::test]