[docs] Empty example section in `onchain-clients.mdx` - fill in or remove?

[callumweb3]

Context

src/pages/build/onchain-clients.mdx, lines ~38-40:

### Example: Fetching the Current Block Number

The following code snippet demonstrates how to fetch and print the current
block number from Ink's testnet:

## Viem - Instructions for Connecting to Ink

The section promises a snippet but provides none.

Given the current situation, I have reached two conclusions:

1. Sections 1 and 3 of the file already contain examples demonstrating how to retrieve the block:

• Ethers.js, step 3: const blockNumber = await provider.getBlockNumber();
• Viem, step 3: const blockNumber = await client.getBlockNumber();

This section might therefore be redundant, so I submitted a PR to remove it: #668

2. If removal is not an acceptable option—even considering the existing examples—I prepared an alternative and added a code block with a working (and tested) example: docs(onchain-clients): add working Ethers.js example to block number section #667

I opened both PRs so you can pick one - happy to close
the other (or you can close it directly).

[callumweb3]

@devknight-ink @lucass555 @przemekink @sergio-inkfnd @CruzMolina @RyLikeBread
If you have a spare minute, please check!