add Haskell snippet for State monad to manage mutable state

Author: ACR1209

snippets/haskell/monads/state-monad.md

@@ -0,0 +1,25 @@
+---
+title: State Monad
+description: Managing mutable state using the State monad.
+author: ACR1209
+tags: haskell, monads, state, state-management
+---
+
+```hs
+import Control.Monad.State
+
+increment :: State Int Int
+increment = do
+    count <- get
+    put (count + 1)
+    return count
+
+main :: IO ()
+main = do
+    let (res1, intermediateState) = runState increment 0
+    print res1      -- Output: 0
+    let (result, finalState) = runState increment intermediateState
+    print result    -- Output: 1
+    print finalState  -- Output: 2
+
+```