Add a dev/offline debug mode

[Slin Lee]

This would mock the responses from polygonscan. The simpler the better.

Simple idea:

• add var in .env.local mock_data, default to false
• when true, replace the requests in polygon.ts with a hardcoded object with realistic data.

This could be used for testing and dev without needing to hit the real polygonscan api.

[Sahil Lavingia]

Attempt coming...