fix: check for LinkML base type "Decimal" on loading changesheet

[dwinston]

Description

Because "Decimal" is not a Python builtins type, and because (py)mongo does not natively json-encode decimal values, and furthermore because existing behavior assumes decimal values will be supplied as floats (as JSON does not support decimals), added case to coerce decimal-typed values to float, and left inline comment explaining decision and options for decimal support in future.

Fixes #613

Type of change

Please delete options that are not relevant.

• [x] Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration, if it is not simply make up-test && make test-run.

• [x] test test_changesheet_update_slot_with_range_decimal with supporting files in tests/files

Configuration Details: none

Definition of Done (DoD) Checklist:

• [x] My code follows the style guidelines of this project (have you run black nmdc_runtime/?)
• [x] I have performed a self-review of my code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have added tests that prove my fix is effective or that my feature works, incl. considering downstream usage (e.g. https://github.com/microbiomedata/notebook_hackathons) if applicable.
• [x] New and existing unit and functional tests pass locally with my changes (make up-test && make test-run)