Optimize: cache JsonSerializerOptions and reduce StringBuilder overhead

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

@@ -108,16 +108,18 @@ type Document with
             let escaped = StringBuilder(s.Length + 2)
             escaped.Append('"') |> ignore
             for c in s do
-                match c with
-                | '"' -> escaped.Append("\\\"") |> ignore
-                | '\\' -> escaped.Append("\\\\") |> ignore
-                | '\b' -> escaped.Append("\\b") |> ignore
-                | '\f' -> escaped.Append("\\f") |> ignore
-                | '\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 -> escaped.Append(c) |> ignore
+                let appendStr =
+                    match c with
+                    | '"' -> "\\\"" 
+                    | '\\' -> "\\\\"
+                    | '\b' -> "\\b"
+                    | '\f' -> "\\f"
+                    | '\n' -> "\\n"
+                    | '\r' -> "\\r"
+                    | '\t' -> "\\t"
+                    | c when c < '\u0020' -> sprintf "\\u%04X" (int c)
+                    | c -> string c
+                escaped.Append(appendStr) |> ignore
             escaped.Append('"').ToString()
         let withQuotes = escapeGraphQLString
         let rec printValue x =

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

@@ -21,17 +21,18 @@ module SchemaId =
     let private formatByteAsLowerHex (value : byte) =
         value.ToString("x2", System.Globalization.CultureInfo.InvariantCulture)
 
+    let private jsonOptions = JsonSerializerOptions(
+        WriteIndented = false,
+        DefaultIgnoreCondition = System.Text.Json.Serialization.JsonIgnoreCondition.Never
+    )
+    
     /// <summary>
     /// Computes a deterministic schema identifier from an introspection schema.
     /// </summary>
     /// <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(
-            WriteIndented = false,
-            DefaultIgnoreCondition = System.Text.Json.Serialization.JsonIgnoreCondition.Never
-        )
-        let json = JsonSerializer.Serialize(introspectionSchema, options)
+        let json = JsonSerializer.Serialize(introspectionSchema, jsonOptions)
         let jsonBytes = Encoding.UTF8.GetBytes json
         use sha256 = SHA256.Create()
         let hash = sha256.ComputeHash jsonBytes