switch from slab to slotmap for tasks to fix that ABA problem (#2488)

Cargo.lock

@@ -2253,6 +2253,7 @@ dependencies = [
  "rustversion",
  "serde",
  "slab",
+ "slotmap",
  "tokio",
  "tracing",
  "tracing-fluent-assertions",
@@ -8343,6 +8344,16 @@ dependencies = [
  "rustc-hash",
 ]
 
+[[package]]
+name = "slotmap"
+version = "1.0.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dbff4acf519f630b3a3ddcfaea6c06b42174d9a44bc70c620e9ed1649d58b82a"
+dependencies = [
+ "serde",
+ "version_check",
+]
+
 [[package]]
 name = "smallvec"
 version = "1.13.2"