Use the thread-pool record for the default timeout

Rather than a parameter.

knots/thread-pool.scm

@@ -151,7 +151,9 @@ from there, or #f if that would be an empty string."
   thread-pool?
   (channel             thread-pool-channel)
   (arguments-parameter thread-pool-arguments-parameter)
-  (proc-vector         thread-pool-proc-vector))
+  (proc-vector         thread-pool-proc-vector)
+  (default-checkout-timeout
+    thread-pool-default-checkout-timeout))
 
 (define* (make-thread-pool size
                            #:key
@@ -163,7 +165,8 @@ from there, or #f if that would be an empty string."
                            (log-exception? (const #t))
                            (expire-on-exception? #f)
                            (name "unnamed")
-                           (use-default-io-waiters? #t))
+                           (use-default-io-waiters? #t)
+                           default-checkout-timeout)
   "Return a channel used to offload work to a dedicated thread.  ARGS are the
 arguments of the thread pool procedure."
   (define param
@@ -349,11 +352,9 @@ arguments of the thread pool procedure."
 (define thread-pool-timeout-error?
   (record-predicate &thread-pool-timeout))
 
-(define %thread-pool-default-timeout
-  (make-parameter 30))
-
 (define* (call-with-thread record proc #:key duration-logger
-                           (timeout (%thread-pool-default-timeout))
+                           (timeout (thread-pool-default-checkout-timeout
+                                     record))
                            (channel (thread-pool-channel record)))
   "Send PROC to the thread pool through CHANNEL.  Return the result of PROC.
 If already in the thread pool, call PROC immediately."