Signac: Improve Sync Data Structures

Signac is a data management framework named after the painter Paul Signac, whose colourful pointillist style resembles a collection of data "points". The signac framework is designed to help researchers design, manage, and execute computational studies. The core data management package signac helps users track data and metadata for file-based workflows (e.g. large molecular simulations) with features for searchability, collaboration, reproducibility, and archival. It stores the data in a JSON file using SyncedAttrDict and JSONDict classes. Currently, Signac uses SyncedAttrDict to store the statepoints and JSONDict to store the documents. In this project, the aim will be to unify the synced collection classes and improve buffering, synchronization and support to different data structures. Also, this project will deal with refractoring the statepoint loading to be lazy.