feat: add requested jobs table

[edparris]

This change adds a new job status table to the ModelRunner database module. This table will be used by a future load based scheduler as temporary storage for image processing jobs that have been pulled from the SQS queue but are not completed.

Note that this table is implemented using different DDB utilities than our other tables. Instead of using the DDBHelper this class interacts with the boto3 DynamoDB table resource directly. The intent was to provide more robust encapsulation for behaviors like conditional updates and table scans. Generalizing those operations to a helper class risks unexpected side effects if those utilities are updated when tuning future tables. Each row is implemented as a dataclass (ImageRequestStatusRecord) but the reusable logic of converting dataclasses to/from dictionaries that can be used as DynamoDB Items is injected using a new Mixin, DataclassDDBMixin. This makes it easy to reuse truly generic logic (e.g. converting numeric values to Decimals to ensure DDB compatibility) with very little overhead.

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[drduhe]

Looks good overall - I will follow up in slack about whether it makes sense to have this table variant from our others using the Mixin, but I do like the approach!

[drduhe]

Can we update these "Any" type hints to reflect the supported operators? I see in the comments we mention it's an int or float but probably support Decimal as well?

[edparris]

They are Any types. If you send a value in that isn't a numeric it is still a valid parameter it just isn't modified.

[drduhe]

Same

[edparris]

Same

[drduhe]

Following our organizational pattern it might be nice to move this out into it's own file since it is a class rather than a function and call it dataclass_ddb_mixin.py

[edparris]

I'll rename the whole thing to dataclass_ddb_mixin.py. The one class per file thing is a Java convention not a Python one and we have plenty of cases where classes/functions/etc. are all grouped meaningfully under a single module.

[drduhe]

LGTM