feat: add request_block_headers_from_peer to RequestSender

[xdustinface]

Add SendMessageToPeer variant to NetworkRequest and request_block_headers_from_peer to RequestSender so sync managers can request block headers from specific peers.

Based on:

• refactor: extract shared send_message_to_peer helper #488

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[github-actions]

This PR has merge conflicts with the base branch. Please rebase or merge the base branch into your branch to resolve them.

[xdustinface]

Part of #490 now.