Enable nested control flow blocks

[fengb3]

Summary

Fixes #11

Adds If, Else, ElseIf, For, While, DoWhile, Foreach, Switch, and Try extension methods on CodeOption (the base class) so control flow constructs can be nested inside any block.

Before (broken)

m.For(f =>
{
    f.Switch(s => { ... }); // ❌ Compile error: ForOption has no Switch method
});

After (works)

m.For(f =>
{
    f.Switch(s =>           // ✅ Now works via CodeOption extension
    {
        s.Case(c =>
        {
            c.If(i => { ... });  // ✅ Deep nesting works too
        });
    });
});

Changes

• Code.cs: Added 9 control flow extension methods on CodeOption following the same AddChild pattern as existing methods
• ControlFlowTests.cs: Added 5 new tests covering nesting scenarios:
  • ForContainingSwitch_Issue11 — the exact example from the issue
  • DeepNesting_ForSwitchCaseIf — 3 levels deep
  • WhileContainingFor — loop nesting
  • TryInsideFor — exception handling inside a loop
  • IfElseIfElseInsideFor — conditional branching inside a loop

Backward Compatibility

The existing MethodOptionExtensions methods are not modified. C# overload resolution prefers the more-specific MethodOption overload when called on a MethodOption, so all existing code continues to work unchanged.

Test Results

All 81 tests pass (76 existing + 5 new).

🤞 Generated with Claude Code