support `[+/-]hhmm` and `[+/-]hh` as fixedoffset timezone format

[waitingkuo]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

as mentioned in #2909 by @tustvold
our parsing function for fixedoffset only support format like +09:00 now. i'd like to extend it to support +09 and +0900 as chrono already has this

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[alamb]

label_issue.py automatically added labels {'arrow'} from #2936