Bug and enhancement for accrual periodicity

[jbrown-xentity]

Plans to resolve #16 and #17, and address comments. This replaces #58, which is out of date and doesn't have some necessary changes/upgrades.

I agree @zopalmer14 , this shouldn't be any string. I've limited it to the lists from the different standards, and linked to the documentation in the JSON schema description. Because ISO-8601 is so open and contains so many possibilities, I decided to allow "recurring" type strings but to allow any number or value type without getting too in the weeds on what could possibly be implemented (months, days, time seconds, etc).

Now that we understand the nuance between oneOf and anyOf (oneOf forces it to only match one of the possible validations, which is rare that we want to do), this should be good to go.

This also provides a good starting point for the "complete" dataset example. It's quite extensive, but also isn't fully complete because it ignores every implementation of the "Concept" class, which is itself a whole issue that should be addressed. I also updated the test code to give more detailed and simplified information around things that don't validate. Below is what it looked like before the improvements, the latter after these changes.

Before updates:

Field: temporal
      Error: [{'@type': 'PeriodOfTime', 'startDate': '2024-01-01', 'endDate': '2024-09-30'}] is not valid under any of the given schemas
      Schema path: properties/temporal/anyOf
      Validator: anyOf
      Sub-errors (2 alternatives failed):
        Field: (root)
          Error: [{'@type': 'PeriodOfTime', 'startDate': '2024-01-01', 'endDate': '2024-09-30'}] is not of type 'null'
          Schema path: 0/type
          Validator: type

        Field: 0
          Error: {'@type': 'PeriodOfTime', 'startDate': '2024-01-01', 'endDate': '2024-09-30'} is not valid under any of the given schemas
          Schema path: 1/items/oneOf
          Validator: oneOf
          Sub-errors (3 alternatives failed):
            Field: (root)
              Error: {'@type': 'PeriodOfTime', 'startDate': '2024-01-01', 'endDate': '2024-09-30'} is not of type 'string'
              Schema path: 1/type
              Validator: type

            Field: endDate
              Error: '2024-09-30' is not valid under any of the given schemas
              Schema path: 0/properties/endDate/anyOf
              Validator: anyOf
              Sub-errors (2 alternatives failed):
                Field: (root)
                  Error: '2024-09-30' is not of type 'null'
                  Schema path: 0/type
                  Validator: type

                Field: (root)
                  Error: '2024-09-30' is valid under each of {'format': 'date'}, {'format': 'date-time'}
                  Schema path: 1/oneOf
                  Validator: oneOf


            Field: startDate
              Error: '2024-01-01' is not valid under any of the given schemas
              Schema path: 0/properties/startDate/anyOf
              Validator: anyOf
              Sub-errors (2 alternatives failed):
                Field: (root)
                  Error: '2024-01-01' is not of type 'null'
                  Schema path: 0/type
                  Validator: type

                Field: (root)
                  Error: '2024-01-01' is valid under each of {'format': 'date'}, {'format': 'date-time'}
                  Schema path: 1/oneOf
                  Validator: oneOf

After updates:

FAIL: Dataset/good/comprehensive-dataset.json (expected good, but validation failed)

  Validation errors for Dataset/good/comprehensive-dataset.json:
    temporal: field is not null and [0]: does not match any alternative:
    - endDate: field is not null and '2026' is valid under each of {'format': 'date'}, {'pattern': '^[0-9]{4}$', 'description': 'A year in YYYY format'}, {'format': 'date-time'}
    - expected type 'string'

[neilmb]

LGTM, one copy-pasta fix, but otherwise great.

[neilmb]

Comment (non-blocking): This looks like a copy-paste error.

Suggested change

	"description": "A minimal dataset example with invalid periodicity",
	"description": "A minimal dataset example with a valid periodicity",

[zopalmer14]

Schema changes and examples LGTM. I left one comment on test_json_schema.py but it's trivial