Fix cumulative metrics from forked processes

Fixed

• In collector mode, report counter metrics correctly from processes forked after AppSignal starts, such as Puma workers when using preload_app!. Before this change, applications running several forked processes would lose data points or report incorrect values for them.

Changed

• Update appsignal dependency to 5.0.3.

View the Ruby gem v5.0.3 changelog for more information.