primitives: use alloy `Sealed<Header>` instead of `SealedHeader`

[tcoratger]

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Describe the feature

The current codebase uses the SealedHeader struct:

https://github.com/paradigmxyz/reth/blob/7529d365157edf37622340bf20b7b0edfe1845a0/crates/primitives-traits/src/header/sealed.rs#L13-L24

This is redundant with Alloy's Sealed<Header> type:

https://github.com/alloy-rs/core/blob/4b823f7977fcdc181a0bd04ba1b2c51f7a29b4e2/crates/primitives/src/sealed.rs#L3-L14

After the merge of https://github.com/paradigmxyz/reth/pull/10691, we have multiple unnecessary conversions between Sealed<Header> and SealedHeader when sealing headers, as we now rely on the Alloy consensus Header type.

Task

• Remove SealedHeader from the codebase.
• Re-export and use Sealed<Header> from Alloy consistently.

Related https://github.com/paradigmxyz/reth/pull/10691#discussion_r1771349415

Additional context

No response