Define ParserContext as ref struct

src/GraphQLParser.Tests/ParserTests.Throw.cs

@@ -294,20 +294,36 @@ public void Should_Throw_If_Descriptions_Not_Allowed(string query)
     [Fact]
     public void Should_Throw_On_Unknown_Cases_From_ExpectOneOf()
     {
-        var context = new ParserContext("abc", default);
-        Should.Throw<NotSupportedException>(() => context.ParseNamedDefinition(new[] { "abc" }))
+        Should.Throw<NotSupportedException>(
+            () =>
+            {
+                var context = new ParserContext("abc", default);
+                context.ParseNamedDefinition(new[] { "abc" });
+            })
             .Message.ShouldBe("Unexpected keyword 'abc' in ParseNamedDefinition.");
 
-        context = new ParserContext("abc", default);
-        Should.Throw<NotSupportedException>(() => context.ParseOperationType(new[] { "abc" }))
+        Should.Throw<NotSupportedException>(
+            () =>
+            {
+                var context = new ParserContext("abc", default);
+                context.ParseOperationType(new[] { "abc" });
+            })
             .Message.ShouldBe("Unexpected keyword 'abc' in ParseOperationType.");
 
-        context = new ParserContext("abc", default);
-        Should.Throw<NotSupportedException>(() => context.ParseDirectiveLocation(new[] { "abc" }))
+        Should.Throw<NotSupportedException>(
+            () =>
+            {
+                var context = new ParserContext("abc", default);
+                context.ParseDirectiveLocation(new[] { "abc" });
+            })
             .Message.ShouldBe("Unexpected keyword 'abc' in ParseDirectiveLocation.");
 
-        context = new ParserContext("extend abc", default);
-        Should.Throw<NotSupportedException>(() => context.ParseTypeExtension(new[] { "abc" }))
+        Should.Throw<NotSupportedException>(
+            () =>
+            {
+                var context = new ParserContext("extend abc", default);
+                context.ParseTypeExtension(new[] { "abc" });
+            })
             .Message.ShouldBe("Unexpected keyword 'abc' in ParseTypeExtension.");
     }
 }

src/GraphQLParser/ParserContext.Parse.cs

@@ -3,8 +3,8 @@
 
 namespace GraphQLParser;
 
-// WARNING: mutable struct, pass it by reference to those methods that will change it
-internal partial struct ParserContext
+// WARNING: mutable ref struct, pass it by reference to those methods that will change it
+internal ref partial struct ParserContext
 {
     // http://spec.graphql.org/October2021/#Document
     public GraphQLDocument ParseDocument()

src/GraphQLParser/ParserContext.cs

@@ -5,8 +5,9 @@
 
 namespace GraphQLParser;
 
-// WARNING: mutable struct, pass it by reference to those methods that will change it
-internal partial struct ParserContext
+// WARNING: mutable ref struct, pass it by reference to those methods that will change it
+
+internal ref partial struct ParserContext
 {
     private static string[] TopLevelKeywordOneOf { get; set; } = new[]
     {