Add support for pgvector types

[exyi]

• vector is serialized as float32 List (with required elements)
• halfvector is also serialized either as float32 List, or the new Parquet float16 if enabled with an option
• sparsevec is serialized as uint32 -> float32 Map (maybe we should add an option to make it a dense vector?)
• bit is already supported (they just add indexes to a built-in postgres type)

Resolves #28