Language: Traits, abstract classes, and interfaces

[PurHur]

Problem

Compiler.php asserts no extends/implements (#101). Traits and abstract methods are unsupported.

Goal

Single inheritance + interface method checks + horizontal trait composition (subset).

Tasks

• Remove asserts; compile extends / implements metadata
• Trait flattening at compile time
• Abstract method enforcement at instantiate
• VM dispatch table for trait precedence

Acceptance

trait T { public function f(): int { return 1; } }
class C { use T; }
(new C)->f() === 1