(feat): [types] require credentials when initializing HumeClient

[twitchard]

Makes two changes to the HumeClient defined In wrapper (i.e. it's controlled manually, not fern-generated).

1. Remove expressionMeasurement override I removed the redefinition of expressionMeasurement and _expressionMeasurement. This is identical to what is in the parent FernClient class, so seemed needless to me. never mind, I was just confused.
2. I redefined the HumeClient.Options type to always require either apiKey or accessToken. We want to prevent users from initializing the client without credentials because this will result in errors further downstream when they attempt to make requests / open connections.

Union of intersection can be confusing, I tested things out here.