more caching in parsed events

Large files require reprocessing once served, adding a way to cache the heatmap module is a big time saver, e.g. trace_event/heatmap can store the genreated namedtuple into a JSON so when called again the existing JSON is just loaded; tried this with a 10GB file, response went down from 2 minutes to 10 seconds. This plus a larger response.cache_control.max_age when responding can reduce greatly the loading time of previously parsed events not to say lowers the resource utilization in the service

# draft on how this can be implemented
def cpuprofile_read_offsets(file_path):
...
    offsets = []
    start_time = None
    end_time = None
    try:
        with open(f"{file_path}.json", "r") as f:
            offsets_collection = collections.namedtuple('offsets', ['start', 'end', 'offsets'])
            res = offsets_collection(**json.load(f))
            return res
    except Exception:
        pass
    ...
    # store the res into a JSON somewehere before returning res
    try:
        with open(f"{file_path}.json", "w+") as f:
            json.dump(res._asdict(), f)
    except Exception:
        pass
    return res