added the cubit and fake repo for change phone number process

[divy-arpit]

Fixes #50

Description

Added the cubit for the change number process along with a fake repository to emulate the entire process

Type of Change: (Delete irrelevant options)

• Code

Code/Quality Assurance Only (Delete irrelevant options)

• New feature (non-breaking change which adds functionality pre-approved by mentors)

How Has This Been Tested?

Tested successfully on local machine

Checklist:

• My PR follows the style guidelines of this project
• I have performed a self-review of my own code or materials
• I have commented my code or provided relevant documentation, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• Any dependent changes have been merged
• I have added one/more required dependencies
• I have formatted the code using dart format (dartfmt)

Code/Quality Assurance

• My changes generate no new warnings
• My PR currently breaks something (fix or feature that would cause existing functionality to not work as expected)
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Mention the dependencies/packages/plugins that have been added (if any)