Cleaning up `sqlite-vector`

[asg017]

• [ ] Deprecate:
  • [ ] vector_from_blob
  • [ ] vector_to_blob
  • [ ] VECTOR_BLOB_HEADER_BYTE and alike
• [ ] fix/re-think:
  • [ ] xValueAsVector - maybe output a data pointer + size and not a std::vector, for better ABI?
  • [ ] xResultVector - take in a data pointer and size?
  • [ ] Maybe xResultVector for json/bytes?
  • [ ] sqlite3_create_function_v2 on "vector0" weirdness