docs: add PublicNode to Unichain node providers

[3eph1r0th]

Summary

Adds PublicNode to the Unichain node providers page.

PublicNode by Allnodes provides fast, free, and privacy-first RPC endpoints for Unichain. Endpoints: https://unichain.publicnode.com/

Type of change

• Fix (typo, broken link, incorrect or outdated content)
• New content (guide, page, code example)
• Update to existing content
• Other

How has this been verified?

Links checked; the block follows the existing provider structure.

Applicable screenshots

None.

[github-actions]

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[github-actions]

This Sepolia link (https://unichain.publicnode.com?sepolia) points to the exact same host as the mainnet link above, with a query string (?sepolia) tacked on that doesn't correspond to any real parameter — it will just load the mainnet endpoint. PublicNode's usual convention for testnets is a distinct subdomain, e.g. unichain-sepolia.publicnode.com (matching patterns like ethereum-sepolia.publicnode.com). Please verify the actual Sepolia endpoint with PublicNode/Allnodes and fix this link — as-is it looks like a broken/incorrect URL rather than a real testnet endpoint.

[github-actions]

Review summary

Content-only change adding a PublicNode entry to the Unichain node providers page, following the existing structure of the other provider sections. Overall the addition matches the file's format (heading, description, "Supported networks" list).

One issue flagged inline: the Sepolia testnet link (https://unichain.publicnode.com?sepolia) is identical to the mainnet link except for a dangling ?sepolia query string that doesn't do anything — it will resolve to the same mainnet endpoint. PublicNode typically uses a distinct subdomain for testnets (e.g. unichain-sepolia.publicnode.com, mirroring ethereum-sepolia.publicnode.com). Please verify the correct Sepolia RPC URL with PublicNode/Allnodes before merging.

No other broken links, formatting, or frontmatter issues found.