[FEATURE] Add support for AdditionalVocabulary in models

[TudorCRL]

Which SDK is this feature request for?

• [ x] speechmatics-rt (Real-Time SDK)
• [ x] speechmatics-batch (Batch SDK)
• Both SDKs
• General/Repository

Is your feature request related to a problem? Please describe.
We need support for additional vocabulary in the form of actual data classes

Describe the solution you'd like
data classes

Describe alternatives you've considered
N/A

Use case
Describe the specific use case or scenario where this feature would be beneficial:

• What are you trying to accomplish?
• How would this feature improve your workflow?
• Who would benefit from this feature?

Related issues/PRs
Link any related issues or pull requests:

• Closes #
• Related to #

Priority/Impact
How important is this feature to you?

• Critical - blocking current work
• High - would significantly improve workflow
• Medium - nice to have improvement
• Low - minor enhancement