Validator does not recognize years as being divisible into months

[uwagura]

Describe the bug
When you try to run fre pp validate with history_segment: P1M and pp_chunk_a: P1Y, you'll get an error that says that pp_chunk_a should be evenly divisible by the size of the history segment

To Reproduce
Add the above key value pairs to your pp yaml

Expected behavior
The validator should recognize months as being divisible by years and accept PXM as a history segment for any pp chunk of the form PNY if 12*N is divisible by X.

Additional context
This issue seems to stem from how the metomi.isodatetime.parser interprets months - it assumes all months are 30 days long, so when we try to check if a year (which metomi interprets as 365 days) is divisible by months, we get false in the following function:

fre-workflows/meta/lib/python/macros/chunkcheck.py

Lines 23 to 31 in c18dedd

	def is_multiple_of(self, big_chunk, small_chunk):
	'''Takes in chunk value e.g P1Y and the chunk reference value from HISTORY_SEGMENT, returns True or False based on the validation to check if the former is a multiple of the latter'''
	big_chunk_days = big_chunk.get_days_and_seconds()[0]
	small_chunk_days = small_chunk.get_days_and_seconds()[0]
	if big_chunk_days % small_chunk_days == 0:
	return True
	else:
	return False

[ceblanton]

Thanks! Completely agree, great catch. @kiihne-noaa started looking at this in #21 and a solution looks straightforward.