Fix Assert extension signatures and keep test helper usage

Agent-Logs-Url: https://github.com/fsprojects/FSharp.Azure.Cosmos/sessions/6f71a1f0-316c-4294-88a6-23f8995238fc

Co-authored-by: xperiandri <2365592+xperiandri@users.noreply.github.com>

Author: Copilot

tests/Cosmos.Tests/Assert.fs

@@ -8,30 +8,30 @@ module AssertExtensions =
 
     type Assert with
 
-        static member WantSome (value, [<Optional>] message) =
+        static member WantSome (value, [<Optional>] message : string | null) =
             match value with
             | Some some -> some
             | None ->
                 Assert.Fail (message)
                 Unchecked.defaultof<_>
 
-        static member IsSome (value, [<Optional>] message) = Assert.WantSome (value, message) |> ignore
+        static member IsSome (value, [<Optional>] message : string | null) = Assert.WantSome (value, message) |> ignore
 
-        static member IsNone (value, [<Optional>] message) =
+        static member IsNone (value, [<Optional>] message : string | null) =
             match value with
             | Some _ -> Assert.Fail (message)
             | None -> ()
 
-        static member WantValueSome (value, [<Optional>] message) =
+        static member WantValueSome (value, [<Optional>] message : string | null) =
             match value with
             | ValueSome some -> some
             | ValueNone ->
                 Assert.Fail (message)
                 Unchecked.defaultof<_>
 
-        static member IsValueSome (value, [<Optional>] message) = Assert.WantValueSome (value, message) |> ignore
+        static member IsValueSome (value, [<Optional>] message : string | null) = Assert.WantValueSome (value, message) |> ignore
 
-        static member IsValueNone (value, [<Optional>] message) =
+        static member IsValueNone (value, [<Optional>] message : string | null) =
             match value with
             | ValueSome _ -> Assert.Fail (message)
             | ValueNone -> ()
@@ -45,7 +45,7 @@ module AssertExtensions =
                 | message -> Assert.Fail ($"'{message}': {error}")
                 Unchecked.defaultof<_>
 
-        static member IsOk (value, [<Optional>] message) = Assert.WantOk (value, message) |> ignore
+        static member IsOk (value, [<Optional>] message : string | null) = Assert.WantOk (value, message) |> ignore
 
         static member WantError (value, [<Optional>] message : string | null) =
             match value with
@@ -56,17 +56,17 @@ module AssertExtensions =
                 | message -> Assert.Fail ($"'{message}': {value}")
                 Unchecked.defaultof<_>
 
-        static member IsError (value, [<Optional>] message) = Assert.WantError (value, message) |> ignore
+        static member IsError (value, [<Optional>] message : string | null) = Assert.WantError (value, message) |> ignore
 
         static member inline IsDefaultOf< ^T> (value : ^T, [<Optional>] message : string) =
             Assert.AreEqual (box value, box Unchecked.defaultof< ^T>, message)
 
-        static member inline OkEquals< ^R, 'E> (expected : ^R, actual : Result< ^R, 'E >, [<Optional>] message) =
+        static member inline OkEquals< ^R, 'E> (expected : ^R, actual : Result< ^R, 'E >, [<Optional>] message : string | null) =
             Assert.AreEqual (box expected, box (Assert.WantOk (actual, message)), message)
 
-        static member inline ErrorEquals<'R, ^E> (expected : ^E, actual : Result<'R, ^E>, [<Optional>] message) =
+        static member inline ErrorEquals<'R, ^E> (expected : ^E, actual : Result<'R, ^E>, [<Optional>] message : string | null) =
             Assert.AreEqual (box expected, box (Assert.WantError (actual, message)), message)
 
-        static member FailWithData<'T> ([<Optional>] message) =
+        static member FailWithData<'T> ([<Optional>] message : string | null) =
             Assert.Fail (message)
             Unchecked.defaultof<'T>