fix alignment event target

[axlEscalada]

Fixes #1250

Issue

EventTarget.constructor() used arena.create() which only allocates memory without initializing struct fields. This left the vtable pointer uninitialized, causing alignment panics when js created EventTarget instances.

Testing

• Added test verifying EventTarget constructor properly initializes vtable and allows event dispatch
• Verified github.com loads without crashes

[github-actions]

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[axlEscalada]

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