Prevent additional network calls when embed script injected more than once

[hopsoft]

User Story

As a publisher, I want a single ad to render even if I accidentally include the embed script more than once so that I don't defraud the system.

Description

Including the embed script more than once triggers multiple network requests for ads and their corresponding pixels. We should detect this and prevent it.

Acceptance Critera

Embedding the script more than once should behave as if it was only included once.