feat(tempo): add sender scoped transaction hashes

[0xrusowsky]

Motivation

Tempo's TIP-1034 channel opens bind channel identity to the tx via an expiringNonceHash:

keccak256(encodeForSigning || sender)

this gives the precompile its replay/same-transaction semantics, but it means viem clients need a way to compute the exact sender-scoped hash before signing the initial voucher.

this depends on wevm/ox#246, which exposes the Tempo transaction signing preimage from ox.

Solution

add Tempo helpers for deriving the sender-scoped transaction hash:

Transaction.encodeForSigning(transaction): Hex
Transaction.getSenderScopedHash(transaction, { sender }): Hex

getSenderScopedHash hashes the Tempo signing preimage together with the resolved sender address. getExpiringNonceHash and getChannelOpenContextHash are exported as aliases for the same TIP-1034-derived value.

this also refactors Tempo serialization to share the same internal envelope normalization used by encodeForSigning, preserving the existing fee-payer behavior where feePayer: true leaves fee token selection to the fee payer.

Tests

• keccak256(encodeForSigning(tx)) matches the ox Tempo sender signing payload.
• encodeForSigning is stable across sender/fee-payer signatures and fee-payer-selected fee token changes when the sender does not commit to the fee token.
• getSenderScopedHash / getExpiringNonceHash / getChannelOpenContextHash match keccak256(encodeForSigning(tx) || sender).

Notes

opened as draft because this branch uses a local ox@0.14.20 patch containing wevm/ox#246, so CI is expected to fail until the ox change lands and viem can depend on the published version.

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