[Bitstream][CAS] Enable BitstreamWriter and BitstreamReader to use CAS as a backing storage

[SanjayMarreddi]

• This PR is basically a draft with the pseudo-code to explain the design/thought process as a part of the GSoC 2024 project proposal.
• Once the project starts, we will use better data structures, better naming for variables, and even better design.
• To have the flexibility of seeing diff via Git, I edited the existing files BitstreamWriter.h & BitstreamReader.h instead of creating respective CAS backed files.