fix: deserialize Id-suffixed tracking option keys

[miachillgood]

Summary

• allow accounting model deserialization to fall back from ...ID to ...Id keys
• add a regression test covering TrackingOptionId inside invoice line-item tracking data

Why

#777 reports that trackingOptionID is defined in the SDK types but stays undefined when getInvoices() returns tracking data.

The generated accounting deserializer currently only reads exact ...ID keys. When the API response uses an ...Id variant, the value is dropped during deserialization.

Testing

• npm test -- --runInBand src/test/objectSerializer.spec.ts
• npm run build

Closes #777