Ensure deterministic JSON serialization and use lowercase hex for Unicode escapes

Agent-Logs-Url: https://github.com/fsprojects/FSharp.Data.GraphQL/sessions/ce0fba11-9043-452f-b948-e03c8b644f26

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

Author: Copilot

src/FSharp.Data.GraphQL.Shared/AstExtensions.fs

@@ -118,7 +118,7 @@ type Document with
                     | '\r' -> "\\r"
                     | '\t' -> "\\t"
                     | c when c < '\u0020' ->
-                        let hex = (int c).ToString("X4", CultureInfo.InvariantCulture)
+                        let hex = (int c).ToString("x4", CultureInfo.InvariantCulture)
                         "\\u" + hex
                     | c -> string c
                 escaped.Append(appendStr) |> ignore

src/FSharp.Data.GraphQL.Shared/ValidationResultCache.fs

@@ -23,7 +23,9 @@ module SchemaId =
 
     let private jsonOptions = JsonSerializerOptions(
         WriteIndented = false,
-        DefaultIgnoreCondition = System.Text.Json.Serialization.JsonIgnoreCondition.Never
+        DefaultIgnoreCondition = System.Text.Json.Serialization.JsonIgnoreCondition.Never,
+        PropertyNamingPolicy = null,
+        Encoder = System.Text.Encodings.Web.JavaScriptEncoder.UnsafeRelaxedJsonEscaping
     )
 
     /// <summary>