Leios N: add field names to Reception

Replace the positional definition of `Reception` with named fields
`receivalTimes` and `received`:

    data Reception a = MkReception
      { receivalTimes :: !(IntMap Time)
      , received      :: !a
      }

Positional pattern matches continue to work; the fields just make
record-style access available where it reads better.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: ch1bo

network-mux/src/Network/Mux/Channel.hs

@@ -89,7 +89,9 @@ data Channel m a = Channel {
   }
 
 -- | A received value paired with the per-chunk arrival times.
-data Reception a = MkReception !(IntMap Time) !a
+data Reception a = MkReception { receivalTimes :: !(IntMap Time)
+                               , received      :: !a
+                               }
   deriving (Foldable, Functor, Traversable)
 
 -- | Given an isomorphism between @a@ and @b@ (in Kleisli category), transform