fix(auth): apply expiryMargin buffer to hasExpired check in setSession() (#1331)

* Initial plan

* fix(auth): apply expiryMargin buffer to hasExpired check in setSession()

Co-authored-by: grdsdev <5923044+grdsdev@users.noreply.github.com>
Agent-Logs-Url: https://github.com/supabase/supabase-flutter/sessions/80e8e775-47d3-4e08-aa75-07f715c27411

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: grdsdev <5923044+grdsdev@users.noreply.github.com>

Author: Copilot

packages/gotrue/lib/src/gotrue_client.dart

@@ -778,7 +778,8 @@ class GoTrueClient {
     // Throws AuthInvalidJwtException if the token is malformed.
     final decoded = decodeJwt(accessToken);
     final exp = decoded.payload.exp;
-    final hasExpired = exp == null || exp <= timeNow;
+    final hasExpired =
+        exp == null || exp <= timeNow + Constants.expiryMargin.inSeconds;
 
     if (hasExpired) {
       return await _callRefreshToken(refreshToken);