refactor: Remove unnecessary SQL.UsageError parameter from PoolAcqTimeoutObs

PoolAcqTimeoutObs is always created with SQL.AcquisitionTimeoutUsageError so the parameter does not provide any useful information.
On the other hand, it complicates debouncing logic in Logger as logWithDebounce has to lazily create the debouncer (which is error prone and hence the logic has a race condition).

This change removes the parameter from PoolAcqTimeoutObs. It is a prerequisite to simplifying logWithDebounce.

src/PostgREST/Observation.hs

@@ -59,7 +59,7 @@ data Observation
   | QueryErrorCodeHighObs SQL.UsageError
   | QueryPgVersionError SQL.UsageError
   | PoolInit Int
-  | PoolAcqTimeoutObs SQL.UsageError
+  | PoolAcqTimeoutObs
   | HasqlPoolObs SQL.Observation
   | PoolRequest
   | PoolRequestFullfilled
@@ -140,8 +140,7 @@ observationMessage = \case
      "Config reloaded"
   PoolInit poolSize ->
      "Connection Pool initialized with a maximum size of " <> show poolSize <> " connections"
-  PoolAcqTimeoutObs usageErr ->
-    jsonMessage usageErr
+  PoolAcqTimeoutObs -> jsonMessage SQL.AcquisitionTimeoutUsageError
   HasqlPoolObs (SQL.ConnectionObservation uuid status) ->
     "Connection " <> show uuid <> (
       case status of