Chore - Refine VectorAnswer for vairous vector_document types

[jaigouk]

Changes

• updated lib/boxcars/boxcar/vector_answer.rb for recent refactoring for vector stores
• updated specs for various vector store types

Why?

• vector_answer also needs to be updated
• provide more exampels in the spec and in notebook
• resolves https://github.com/BoxcarsAI/boxcars/issues/84

Test

• irb console result
• specs are green

[jaigouk]

i will open this later when it is ready.

https://github.com/jaigouk/boxcars/pull/4