Add feature to parse duration period

[mohammad-albarham]

What problem are you trying to solve?

Parsing the duration from the text that has the difference between the two dates.

Examples (if relevant)

>>> from maha.parsers.functions import parse_dimension
>>> output = parse_dimension('عن ربع نمو سكان العالم القديم والتحضر بين 1700 و 1900 ميلادي', duration=True)[0].value
>>> output
DurationValue(values=[ValueUnit(value=200, unit=<DurationUnit.YEARS: 7>)], normalized_unit=<DurationUnit.SECONDS: 1>)

Definition of Done

• It must adhere to the coding style used in the defined dimensions, duration dimension.
• The implementation should cover most use cases.
• Adding tests

[TRoboto]

This shouldn't return the difference, rather it would be better to return a new period object for the duration. Something similar to:

DurationPeriod(start=ValueUnit(value=1700, unit=<DurationUnit.YEARS: 7>), end=ValueUnit(value=1900, unit=<DurationUnit.YEARS: 7>))