Handle FORMAT and calls columns, factored out of parse_line

def _handle_calls(self, alts, format_, format_str, arr):
        """Handle FORMAT and calls columns, factored out of parse_line"""
        if format_str not in self._format_cache:
            self._format_cache[format_str] = list(map(self.header.get_format_field_info, format_))
        # per-sample calls
        calls = []
        for sample, raw_data in zip(self.samples.names, arr[9:]):
            if self.samples.is_parsed(sample):
                data = self._parse_calls_data(format_, self._format_cache[format_str], raw_data)
                call = record.Call(sample, data)
                self._format_checker.run(call, len(alts))
                self._check_filters(call.data.get("FT"), "FORMAT/FT", call.sample)
                calls.append(call)
            else:
                calls.append(record.UnparsedCall(sample, raw_data))
        return calls