fix: fixes server timings' precision (#3227)

* test: fix test_io accordingly

src/PostgREST/Response/Performance.hs

@@ -1,3 +1,4 @@
+{-# LANGUAGE NumericUnderscores #-}
 module PostgREST.Response.Performance
   ( ServerTiming (..)
   , serverTimingHeader
@@ -8,6 +9,7 @@ import qualified Network.HTTP.Types    as HTTP
 import           Numeric               (showFFloat)
 import           Protolude
 
+-- | ServerTiming represents the timing data for a request, in seconds.
 data ServerTiming =
   ServerTiming
     { jwt         :: Maybe Double
@@ -19,14 +21,15 @@ data ServerTiming =
   deriving (Show)
 
 -- | Render the Server-Timing header from a ServerTimingData
+-- The duration precision is milliseconds, per the docs
 --
 -- >>> serverTimingHeader ServerTiming { plan=Just 0.1, transaction=Just 0.2, response=Just 0.3, jwt=Just 0.4, parse=Just 0.5}
--- ("Server-Timing","jwt;dur=400000.0, parse;dur=500000.0, plan;dur=100000.0, transaction;dur=200000.0, response;dur=300000.0")
+-- ("Server-Timing","jwt;dur=400.0, parse;dur=500.0, plan;dur=100.0, transaction;dur=200.0, response;dur=300.0")
 serverTimingHeader :: ServerTiming -> HTTP.Header
 serverTimingHeader timing =
   ("Server-Timing", renderTiming)
   where
-    renderMetric metric = maybe "" (\dur -> BS.concat [metric, BS.pack $ ";dur=" <> showFFloat (Just 1) (dur * 1000000) ""])
+    renderMetric metric = maybe "" (\dur -> BS.concat [metric, BS.pack $ ";dur=" <> showFFloat (Just 1) (dur * 1_000) ""])
     renderTiming = BS.intercalate ", " $ (\(k, v) -> renderMetric k (v timing)) <$>
       [ ("jwt", jwt)
       , ("parse", parse)