Set Up Integer Constants and Variable Storage

[kh3rld]

Implement functionality for storing and retrieving integer values in variables, allowing users to assign int values to variables.

Tasks:

• Define syntax and parser rules for variable declarations with int values.
• Implement storage and retrieval methods for integer values in the interpreter’s environment.
• Add unit tests for variable assignment and retrieval, covering redeclaration errors.

Acceptance Criteria:

• Variables can be declared, assigned integer values, and retrieved accurately.
• Errors are returned when redeclaring or reassigning values to incompatible types.