Timezone support

[rien333]

If I read rfc3339 correctly, offsets from UTC can be specified with +0X:00. However, if I manually create a pages.jsonl with such timezone suffices, I receive an error when I run wacz create --pages pages.jsonl -f mywarc.warc.gz:

Traceback (most recent call last):
  File "/usr/bin/wacz", line 8, in <module>
    sys.exit(main())
             ^^^^^^
  File "/usr/lib/python3.12/site-packages/wacz/main.py", line 123, in main
    value = cmd.func(cmd)
            ^^^^^^^^^^^^^
  File "/usr/lib/python3.12/site-packages/wacz/main.py", line 211, in create_wacz
    passed_pages_dict = construct_passed_pages_dict(passed_content)
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/site-packages/wacz/util.py", line 90, in construct_passed_pages_dict
    key = iso_date_to_timestamp(page_dict.pop("ts")) + "/" + url
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/site-packages/warcio/timeutils.py", line 155, in iso_date_to_timestamp
    return datetime_to_timestamp(iso_date_to_datetime(string))
                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/site-packages/warcio/timeutils.py", line 60, in iso_date_to_datetime
    the_datetime = datetime.datetime(*(int(num) for num in nums))
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/site-packages/warcio/timeutils.py", line 60, in <genexpr>
    the_datetime = datetime.datetime(*(int(num) for num in nums))
                                       ^^^^^^^^
ValueError: invalid literal for int() with base 10: ''

pages.jsonl

{"url":"http://example.archive/example.html","title":"Example","ts":"2013-05-07T00:00:00+01:00","mime":"text/html"}

Seems like the case where the timezone suffix is simply Z is handled correctly, though.