feat: Add validation for inline methods in Neo compiler

[Jim8y]

Summary

This PR adds comprehensive validation for methods marked with [MethodImpl(MethodImplOptions.AggressiveInlining)] to prevent compilation issues and ensure correct behavior in Neo smart contracts.

Problem

The current inline implementation in the Neo compiler lacks validation for edge cases that could lead to:

• Infinite expansion with recursive methods
• Incorrect behavior with ref/out parameters
• Excessive code size with large inlined methods

Solution

Added three key validations to the TryProcessInlineMethods method:

1. Recursive Method Detection

• Detects recursive calls within inline methods
• Throws CompilationException when recursion is detected
• Prevents infinite expansion during compilation

2. Ref/Out Parameter Validation

• Checks for ref/out parameters in inline methods
• These cannot be properly inlined with the current stack-based implementation
• Throws CompilationException when ref/out parameters are found

3. Method Size Warning

• Estimates the size of methods marked for inlining
• Warns when inlining large methods (>50 estimated instructions)
• Helps developers avoid excessive code bloat

Changes

• Modified: src/Neo.Compiler.CSharp/MethodConvert/Helpers/ConvertHelpers.cs

  • Added IsRecursiveMethod() helper to detect recursive calls
  • Added EstimateMethodSize() helper to estimate instruction count
  • Added validation logic in TryProcessInlineMethods()

• Added Test Contracts:

  • Contract_Inline_Invalid.cs - Test cases for invalid inline scenarios
  • Contract_Inline_EdgeCases.cs - Comprehensive edge case testing

• Added Unit Tests:

  • UnitTest_Inline_Validation.cs - Validates that compilation fails for invalid cases
  • UnitTest_Inline_EdgeCases.cs - Tests various edge cases

Testing

The PR includes comprehensive test coverage:

• ✅ Recursive method validation
• ✅ Ref/out parameter validation
• ✅ Method size warning
• ✅ Edge cases like parameter shadowing, nested inlines, complex expressions

Impact

• Breaking Change: No
• Performance Impact: Minimal (validation only during compilation)
• Security Impact: Improves contract safety by preventing invalid inline usage

Checklist

• Code follows project style guidelines
• Tests added for new functionality
• All tests pass
• Documentation updated where necessary
• No breaking changes to existing functionality