Extended calculator functionality and improved evaluation logic

[markonnn]

I upgraded the code so the calculator can handle long, complex equations instead of just one simple math expression at a time.

key improvements:

• Implemented a parse_and_calculate method using regular expressions to replace step by step logic. The calculator now handles complex strings
• Added scientific functions (trigonometric, logarithmic, constants, abs, round) and large factorial support: if a number is too big to calculate normally, the calculator now uses a log gamma approximation
• Enabled auto-fix for parentheses to automatically finish equations if a bracket is left open
• Updated the UI with a redesigned layout using frames, added parentheses and backspace buttons and enabled enter key evaluation
• Included unit tests to verify complex expressions and operator behaviour

All existing basic calculator functionality is preserved