Add lazy versions of Text functions

We had `readFile` and `writeFile` fot strict `Text`, but not for
lazy.

Add lazy versions of the same functions, basically, by copy-pasting.

lib/Data/Text/IO/Utf8.hs

@@ -3,7 +3,7 @@
  - SPDX-License-Identifier: MPL-2.0
  -}
 
--- | Data Text IO for the modern world.
+-- | "Data.Text.IO" for the modern world.
 --
 -- Wrappers around simple file reading/writing functions from the
 -- @text@ package that reset the handle encoding to UTF-8.

lib/Data/Text/Lazy/IO/Utf8.hs

@@ -0,0 +1,35 @@
+{- SPDX-FileCopyrightText: 2020 Serokell <https://serokell.io/>
+ -
+ - SPDX-License-Identifier: MPL-2.0
+ -}
+
+-- | "Data.Text.Lazy.IO" for the modern world.
+--
+-- Wrappers around simple file reading/writing functions from the
+-- @text@ package that reset the handle encoding to UTF-8.
+module Data.Text.Lazy.IO.Utf8
+  ( readFile
+  , writeFile
+  ) where
+
+import Prelude hiding (readFile, writeFile)
+
+import Control.Exception.Safe (MonadMask)
+import Control.Monad.IO.Class (MonadIO, liftIO)
+import Data.Text.Lazy (Text)
+
+import qualified Data.Text.Lazy.IO as T
+import qualified System.IO as IO
+
+import qualified System.IO.Utf8 as Utf8
+
+
+-- | Like @readFile@, but assumes the file is encoded in UTF-8, regardless
+-- of the current locale.
+readFile :: MonadIO m => IO.FilePath -> m Text
+readFile path = Utf8.openFile path IO.ReadMode >>= liftIO . T.hGetContents
+
+-- | Like @writeFile@, but encodes the data in UTF-8, regardless
+-- of the current locale.
+writeFile :: (MonadIO m, MonadMask m) => IO.FilePath -> Text -> m ()
+writeFile path = Utf8.withFile path IO.WriteMode . (liftIO .) . flip T.hPutStr