some latency hacks (#30566)

These changes cut some method dependency edges that tend to lead to
invalidations when loading packages.

src/managers.jl

@@ -373,7 +373,7 @@ manage
 struct DefaultClusterManager <: ClusterManager
 end
 
-const tunnel_hosts_map = Dict{AbstractString, Semaphore}()
+const tunnel_hosts_map = Dict{String, Semaphore}()
 
 """
     connect(manager::ClusterManager, pid::Int, config::WorkerConfig) -> (instrm::IO, outstrm::IO)