fix: Field resolvers are mutable

This allows us to modify resolvers after creation, making conversions between AST schemas (that have no resolvers) and executable schemas easier.

Author: NeedleInAJayStack

Sources/GraphQL/Type/Definition.swift

@@ -489,13 +489,19 @@ public struct GraphQLResolveInfo: Sendable {
 
 public typealias GraphQLFieldMap = OrderedDictionary<String, GraphQLField>
 
-public struct GraphQLField: Sendable {
+public struct GraphQLField: @unchecked Sendable {
     public let type: GraphQLOutputType
     public let args: GraphQLArgumentConfigMap
     public let deprecationReason: String?
     public let description: String?
-    public let resolve: GraphQLFieldResolve?
-    public let subscribe: GraphQLFieldResolve?
+
+    /// The resolution logic of the field. This should not be mutated while the schema is being
+    /// used.
+    public var resolve: GraphQLFieldResolve?
+    /// The subscription logic of the field. This should not be mutated while the schema is being
+    /// used.
+    public var subscribe: GraphQLFieldResolve?
+
     public let astNode: FieldDefinition?
 
     public init(