Add Support for Escape Characters in Strings

[maybe-adev]

Extend the string logic in the lexer to allow escape sequences:

• \n → newline

• \t → tab

• " → quote inside string

• \ → backslash

Example:

show("Hello\nWorld")
show("He said \"Hi\" to me")

Tasks Needed:

• Modify lexer to detect \ inside a string

• Convert supported escape chars

• Throw error if escape is invalid

Why this helps:
Makes Pearlen feel more like a real programming language and improves string readability.