feat: Implement conditional control structures (@if, @elseif, @else, @endif)

[benkhalife]

Description

This issue proposes adding conditional control directives to improve the templating syntax. Instead of mixing plain PHP if statements, implementing @if directives will provide a cleaner, modern syntax closer to popular template engines.

Proposed Syntax

@if($user->isAdmin())
    <p>Welcome, Admin!</p>
@elseif($user->isEditor())
    <p>Welcome, Editor!</p>
@else
    <p>Welcome, User!</p>
@endif

Expected Behavior

The compiler should seamlessly translate these directives into standard PHP conditional statements (, , etc.).

Checklist

• Implement parser for @if(...) and @endif.
• Implement parser for @elseif(...) and @else.
• Ensure brackets and expressions inside @if(...) are evaluated safely.
• Add unit tests covering all conditional flows.