Byron: Force startTime in genesis data to be strict

eras/byron/ledger/impl/cardano-ledger-byron.cabal

@@ -243,6 +243,7 @@ library
         contra-tracer,
         cryptonite,
         Cabal-syntax,
+        deepseq,
         digest,
         directory,
         filepath,

eras/byron/ledger/impl/src/Cardano/Chain/Genesis/Data.hs

@@ -29,6 +29,7 @@ import Cardano.Crypto (
  )
 import Cardano.Ledger.Binary
 import Cardano.Prelude
+import Control.DeepSeq ((<$!!>))
 import qualified Data.ByteString as BS
 import qualified Data.ByteString.Lazy as BSL
 import Data.List (lookup)
@@ -48,6 +49,7 @@ import Text.JSON.Canonical (
   parseCanonicalJSON,
   renderCanonicalJSON,
  )
+import Prelude (id)
 
 -- | Genesis data contains all data which determines consensus rules. It must be
 --   same for all nodes. It's used to initialize global state, slotting, etc.
@@ -93,7 +95,7 @@ instance MonadError SchemaError m => FromJSON m GenesisData where
     GenesisData
       <$> fromJSField obj "bootStakeholders"
       <*> fromJSField obj "heavyDelegation"
-      <*> fromJSField obj "startTime"
+      <*> (id <$!!> fromJSField obj "startTime")
       <*> fromJSField obj "nonAvvmBalances"
       <*> fromJSField obj "blockVersionData"
       -- The above is called blockVersionData for backwards compatibility with