feat: Allow FlagEvaluationDetails to be a public API (#79)

## This PR

Small change to enable `FlagEvaluationOptions` to be used during flag
evaluations. Currently the constructor and params were internal APIs so
custom options couldn't be passed in.

---------

Signed-off-by: jescriba <[email protected]>
Signed-off-by: Joshua E. <[email protected]>

Author: jescriba

Sources/OpenFeature/FlagEvaluationOptions.swift

@@ -1,6 +1,15 @@
 import Foundation
 
+/// FlagEvaluationOptions is a struct that enables passing in custom hooks and hints to the flag evaluation process.
 public struct FlagEvaluationOptions {
-    var hooks: [any Hook] = []
-    var hookHints: [String: Any] = [:]
+    public let hooks: [any Hook]
+    public let hookHints: [String: Any]
+
+    public init(
+        hooks: [any Hook] = [],
+        hookHints: [String: Any] = [:]
+    ) {
+        self.hooks = hooks
+        self.hookHints = hookHints
+    }
 }