docs: sync OpenAPI - add evm.md

[Copilot]

Syncs docs/evm.md from Tuned06/subscan-OpenAPI@4ef794f. Adds a guide for EVM smart contract verification on Subscan (Darwinia, Moonbeam, Astar, etc.) covering Remix setup, Standard Input JSON construction, and upload. Also fixes invalid // comments in JSON code block examples.

The other files changed in the referenced commit (Introduction.md, gen-doc.py, subscan.apidog.json) have no counterparts in this repo and were not applied.

Checklist

• Use the owner account that submitted registrar_reserve to sign the project information, and fill in the signature.
• After each update of the project information, please sign the latest data and submit the signature.
• Add a description for your pr, the description includes the original data.
• Fill up the signature of the original data, signature account to Signature Auto check.

Signature Auto check

Para ID Owner & Signature Account:
<REPLACE THE OWNER>

Data that needs to be signed:
file

Signature Hash: <REPLACE THE SIGNATURE>