Allow viem client as EVM signer in xcm-sdk

[mmaurello]

Description

With the latest xcm-sdk version, we allow viem's WalletClient as a signer. Since there is an ongoing tendency for replacing ethers for viem

Checklist

• If this requires translations for the moonbeam-docs-cn repo, I have created a ticket for the translations in Jira
• If pages have been moved around, I have created an additional PR in moonbeam-mkdocs to update redirects
• If pages have been moved around, I have run the move-pages.py script to move the pages and update the image paths on the chinese repo
  • After the script has been run, I have created an additional PR in moonbeam-docs-cn
• If images have been added, I have run the compress-images.py script to compress the images.
• If variables (in variables.yml) need to be updated (such as a name change), I have updated the moonbeam-docs-cn repo to use the new variables
• If this page requires a disclaimer, I have added one

Corresponding PRs

moonbeam-foundation/xcm-sdk#131

After Translation Requirements

• Will need to create PR in moonbeam-docs repo to remove images
• Will need to create PR in moonbeam-docs repo to remove variables
• Will need to create PR in moonbeam-mkdocs repo to add redirects for Chinese site
• No additional PRs are required after the translations are done

Items to be Updated

n/a

[eshaben]

Thanks @mmaurello!!