Fix date omission in span_range() when exact is True

[rkendra]

Pull Request Checklist

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• 🧪 Added tests for changed code.
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Description of Changes

Fixed an edge case that occurred in span_range() that caused the omission of dates when frame = 'month', exact = True, and start.day > 28.

span_range() now exhibits similar behavior to range() in this case where the returned Arrow object from span() is checked against the start date and updated accordingly.

Closes: #1185

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (master@85cd905). Learn more about missing BASE report.
✅ All tests successful. No failed tests found.

Additional details and impacted files

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  Files             ?        10           
  Lines             ?      2350           
  Branches          ?       360           
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  Hits              ?      2350           
  Misses            ?         0           
  Partials          ?         0           

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