Add colored parentheses and compact mode module with compiler directive activation

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This PR implements a new enhanced output module that provides colored parentheses and compact mode functionality for the Lambda Calculus Interpreter. The module can be activated via compiler directives without modifying any existing source files.

Features

🎨 Colored Parentheses

• Each nesting level uses a different color from a palette of 12 colors (Red, Green, Yellow, Blue, Magenta, Cyan + bright variants)
• Uses ANSI escape codes for terminal compatibility
• Greatly improves readability of deeply nested lambda expressions

📦 Compact Mode

• Removes unnecessary parentheses while maintaining mathematical correctness
• Significantly reduces visual clutter in complex expressions
• Example: (λx.(x)) y becomes (λx.x) y

🔧 Drop-in Replacement

The module acts as a complete drop-in replacement that can be enabled entirely through compiler flags:

# Enable colored parentheses only
gcc -DENABLE_ENHANCED_OUTPUT -DENHANCED_OUTPUT_MODE=1 ...

# Enable compact mode only  
gcc -DENABLE_ENHANCED_OUTPUT -DENHANCED_OUTPUT_MODE=2 ...

# Enable both features
gcc -DENABLE_ENHANCED_OUTPUT -DENHANCED_OUTPUT_MODE=3 ...

# Default behavior (no flags needed)
gcc ...

Implementation

The module provides four operation modes:

• Mode 0: Normal (default behavior)
• Mode 1: Colored parentheses only
• Mode 2: Compact formatting only
• Mode 3: Both colored and compact

When enabled, existing expr_to_buffer() calls are automatically replaced with enhanced versions through preprocessor macros, requiring zero code changes.

Files Added

• include/enhanced_output.h - Core interface definitions
• src/enhanced_output.c - Implementation of colored and compact formatting
• include/enhanced_wrapper.h - Drop-in replacement wrapper with macros
• test/test_enhanced_simple.c - Comprehensive test suite
• ENHANCED_OUTPUT_README.md - Complete usage documentation
• Makefile.enhanced - Additional build targets

Example Output

Before (standard):

(λx.(x)) y
(λf.λx.f (f x))

After (colored + compact):

(λx.x) y                    # Red parentheses
λf.λx.f (f x)              # Nested colors: red, green, blue

The module maintains complete backward compatibility and has zero performance impact when disabled.

Fixes #11.

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