Implement OwnershipGraph for Borrowing Rules in Rust

[notJoon]

In this PR, we have implemented the OwnershipGraph data structure to enforce borrowing rules in this language.

Changes made:

1. Implementation of OwnershipGraph: We've introduced a new data structure, OwnershipGraph, which stores variables and their borrowed values in a collections::BTreeMap to maintain a consistent output order. This helps us to understand and verify the borrowing rules for each variable in the language.

2. Introduction of build_ownership_graph function: This function takes a vector of Statements as an argument and generates an OwnershipGraph. This graph will be used to enforce borrowing rules and prevent multiple mutable references or simultaneous mutable and immutable references.

3. Writing Test Cases: We have added comprehensive test cases for the build_ownership_graph function. These tests ensure that our implementation correctly handles variable declarations, borrowing, and the restrictions of Rust's ownership rules. Also, modefied other files tests too.

TODO

• should implement the borrow checker's functionality for nested scope.