Add vtimezone tzinfo implementation

[allenporter]

Add vtimezone tzinfo implementation with the following changes:

• Evaluate rrules for vtimezones
• centralize rrule creation and iterator libraries for rrule evaluation in multiple contexts beyond timeline
• add dtstart and rrule validation based on rfc5545

This change allows you to create datetime objects with a functioning timezone based on the ics input, however currently it is currently not yet used when parsing an ICS file.

Issue #70
Issue #71

[codecov-commenter]

Codecov Report

Merging #94 (53f4b6f) into main (0943cbe) will increase coverage by 0.16%.
The diff coverage is 96.98%.

@@            Coverage Diff             @@
##             main      #94      +/-   ##
==========================================
+ Coverage   96.59%   96.76%   +0.16%     
==========================================
  Files          20       21       +1     
  Lines        1791     1885      +94     
==========================================
+ Hits         1730     1824      +94     
  Misses         61       61              

Impacted Files	Coverage Δ
ical/calendar.py	100.00% <ø> (ø)
ical/timezone.py	96.42% <94.59%> (-2.21%)	⬇️
ical/types.py	96.70% <95.23%> (-0.06%)	⬇️
ical/event.py	96.18% <100.00%> (+0.02%)	⬆️
ical/iter.py	100.00% <100.00%> (ø)
ical/journal.py	100.00% <100.00%> (ø)
ical/timeline.py	95.40% <100.00%> (+1.83%)	⬆️
ical/todo.py	98.36% <100.00%> (+0.02%)	⬆️

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