Add Merge Sort in F#

Merge FSharp/src/Merge.fs

@@ -0,0 +1,10 @@
+module Merge
+
+let rec merge list1 list2 =
+    match list1, list2 with
+    | [], ys -> ys                     // If either list is empty, return the other
+    | xs, [] -> xs
+    | x::xs, y::ys when x <= y ->      // Compare heads of both lists
+        x :: merge xs (y::ys)          // Take smaller element (x) and recurse
+    | x::xs, y::ys ->
+        y :: merge (x::xs) ys          // Otherwise take y and recurse    

Merge FSharp/test/MergeTests.fs

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+module MergeTests
+
+[<Tests>]
+let tests =
+    testList "Merge Tests" [
+        testCase "Merge two sorted lists" <| fun _ ->
+            let result = merge [1;3;5] [2;4;6]
+            Expect.equal result [1;2;3;4;5;6] "Should merge sorted lists"
+
+        testCase "Merge with empty list" <| fun _ ->
+            let result = merge [] [2;4;6]
+            Expect.equal result [2;4;6] "Should handle empty first list"
+    ]

Merge FSharp/test/mergeExample.sln

@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>f# 8.0</TargetFramework>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="src/Merge.fs" />
+    <Compile Include="test/MergeTests.fs" />
+  </ItemGroup>
+  <ItemGroup>
+    <PackageReference Include="Expecto" Version="12.8.403.0" />
+  </ItemGroup>
+</Project>