VoyageAIRerank constructor fix

[Adversarian]

Description

In the new voyageai client, the rerank method does not take truncation as an optional nullable argument. Furthermore, top_n is an optional nullable argument but was defined as a non-optional non-nullable argument previously. This made it so that the construction of the class without all the unrequired arguments would result in a validation error from Pydantic.

This change shouldn't be breaking for all intents and purposes since default values have been supplied where necessary and they will be overridden if otherwise specified. A unit test was developed for this specific case.

Version Bump?

Did I bump the version in the pyproject.toml file of the package I am updating? (Except for the llama-index-core package)

• Yes
• No

Type of Change

Please delete options that are not relevant.

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

How Has This Been Tested?

Your pull-request will likely not be merged unless it is covered by some form of impactful unit testing.

• I added new unit tests to cover this change
• I believe this change is already covered by existing unit tests