Update indexers.mdx : Add Envio

[Jordy-Baby]

Envio’s indexing framework supports devs on Abstract with efficient access to real-time & historical data.

Sync millions of events 2000x faster than RPC. Easy, fast & customizable.

More info: https://envio.dev

Could you please add Envio under the data & indexing section?

Feel free to reach out if you require anything further from our end. jordyn@envio.dev

Thanks! 😺

[cursor]

PR Summary

Low Risk
Docs-only change that adds a new external link and minor formatting; no runtime or security impact.

Overview
Adds a new Envio card/link to ecosystem/indexers.mdx under the Data & Indexing section.

Also reformats the existing card entries (spacing/line breaks) without changing their targets.

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