Change approach for allowing `seg_name` and `seg_len` to be lists

In https://github.com/MIT-LCP/wfdb-python/pull/514 an update was made to allow seg_name and seg_len to be lists. This is needed for writing a MultiSegmentRecord.

@bemoody , suggested an alternate approach:

But I think what we really want is, rather than changing the types in SEGMENT_SPECS, we want to add "seg_name" and "seg_len" to LIST_FIELDS (wfdb/io/record.py, line 1675.)

This issue is being opened to track implementing this alternate approach.

首先检查 wfdb/io/record.py 中约第 1675 行附近的 LIST_FIELDS，以及当前对 SEGMENT_SPECS 的处理方式。当 seg_name 和 seg_len 通过 LIST_FIELDS 进行处理，并且写入 MultiSegmentRecord 仍继续支持它们时，此更改即完成。