Apply code review feedback: use uppercase hex for Unicode escapes and object initializer syntax

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

@@ -116,7 +116,7 @@ type Document with
                 | '\n' -> escaped.Append("\\n") |> ignore
                 | '\r' -> escaped.Append("\\r") |> ignore
                 | '\t' -> escaped.Append("\\t") |> ignore
-                | c when c < '\u0020' -> escaped.AppendFormat("\\u{0:x4}", int c) |> ignore
+                | c when c < '\u0020' -> escaped.AppendFormat("\\u{0:X4}", int c) |> ignore
                 | c -> escaped.Append(c) |> ignore
             escaped.Append('"').ToString()
         let withQuotes = escapeGraphQLString

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

@@ -27,9 +27,10 @@ module SchemaId =
     /// <param name="introspectionSchema">The introspection schema to hash.</param>
     /// <returns>A lowercase hexadecimal SHA-256 hash string that uniquely identifies the schema structure.</returns>
     let fromIntrospectionSchema (introspectionSchema : IntrospectionSchema) =
-        let options = JsonSerializerOptions()
-        options.WriteIndented <- false
-        options.DefaultIgnoreCondition <- System.Text.Json.Serialization.JsonIgnoreCondition.Never
+        let options = JsonSerializerOptions(
+            WriteIndented = false,
+            DefaultIgnoreCondition = System.Text.Json.Serialization.JsonIgnoreCondition.Never
+        )
         let json = JsonSerializer.Serialize(introspectionSchema, options)
         let jsonBytes = Encoding.UTF8.GetBytes json
         use sha256 = SHA256.Create()