feat: Add pointer support

[tacheraSasi]

This PR introduces basic pointer support to VintLang, allowing for more advanced data manipulation.

Key Features:

Address-of Operator (&): Get a pointer to the value of a variable.
Dereference Operator (*): Access the value a pointer refers to.
Implementation Details:

Lexer: Added AMPERSAND (&) and ASTERISK (*) as tokens. & is now correctly tokenized as a single operator.
Parser: Registered & and * as prefix operators, allowing expressions like &x and p.
Object System: Introduced a new object.Pointer type to represent pointers at runtime.
Evaluator: Implemented logic to handle the creation of pointers (&) and dereferencing (). Includes defensive checks for nil and non-pointer values.
Documentation: Added docs/pointers.md explaining the new feature, its syntax, and its current limitations (value pointers, not variable references).
Example Usage:

let x = 42
let p = &x // p is a pointer to the value of x

print(p) // Prints the pointer's representation
print(*p) // Prints 42
This feature lays the groundwork for more complex memory management and data structure implementations in the future.