fix(FCM.Error): handle multiple elements in "details" list with recursive parsing

[caruspi]

Description

The current implementation of the parse/1 function in Pigeon.FCM.Error does not correctly handle cases where the "details" list contains multiple elements. It only matches when only one element is in the list and has an "errorCode", causing certain errors to be mapped as :unknown_error instead of the expected values.

In our production logs, we are seeing a large number of :unknown_error entries with the following error message:

%{
  "code" => 404,
  "details" => [
    %{
      "@type" => "type.googleapis.com/google.firebase.fcm.v1.FcmError",
      "errorCode" => "UNREGISTERED"
    },
    %{
      "@type" => "type.googleapis.com/google.firebase.fcm.v1.ApnsError",
      "reason" => "Unregistered",
      "statusCode" => 410
    }
  ],
  "message" => "Requested entity was not found.",
  "status" => "NOT_FOUND"
}

This should be mapped as :unregistered, but the current implementation fails to find the "errorCode" because multiple elements are in the list.

Solution

This PR refactors the parse/1 function to use a recursive approach for parsing the "details" list. It now iterates through all elements until it finds one with an "errorCode" and correctly maps it to the corresponding atom. If no "errorCode" is found, it falls back to checking the "status" field.