feat(anvil.js): Add support for specifying headers in fork mode

[jnsdls]

This adds the ability to pass headers for the fork url to the underlying anvil instance.

This does not seem to be documented in the anvil reference however it is available in anvil as a command line option

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PR-Codex overview

This PR enhances the @viem/anvil package by adding support for specifying headers in fork mode and updating the toArgs function to handle nested objects.

Detailed summary

• Added forkHeader option to specify headers in fork mode
• Updated toArgs function to handle nested objects in options

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[changeset-bot]

🦋 Changeset detected

Latest commit: d9c9b36

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@viem/anvil	Patch

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