Better page packing

[Scooletz]

Provide capability to pack data into a page in a better way. Use the page approach where the slice of data responsible for storing kv pairs grows from two directions to the center:

1. id entries, grow ➡, from 0 to the center and capture basic lookup information
2. payload, grow ⬅ , from the end to the center and capture payload

Additional materials:

1. PostgreSQL: bufpage.c
2. PostgresSQL docs
3. Andy Pavlo lecture: 03 - Database Storage 1 (CMU Intro to Database Systems / Fall 2022

This implementation might not necessarily deal with all the aspects, but should be similar to the slotted pages. The indexing aspect might left as is now.