fix(evm): prefer EIP-3009 authorization

[Xeift]

Prefer authorization for tokens known to support EIP-3009 when no splits are requested.
Permit2 remains the preferred option otherwise.

Refs #264

[chopmob-cloud]

No objection to preferring type="authorization" for EIP-3009 tokens when
there are no splits. The line you draw (authorization for simple single
transfers, Permit2 for splits and server-paid fees) is the right one, since
EIP-3009 transferWithAuthorization cannot express atomic splits.

One coordination note: #313 also edits this section of
draft-evm-charge-00.md. It removes the redundant externalId from the
Permit2 PaymentWitness, because every request field (including externalId
when present) is already bound through challengeHash. That change is
orthogonal to the preference change here (witness cleanup vs recommended
type), and I confirmed #313 rebases cleanly on top of this PR with no
conflicts. Happy to sequence #313 after this one merges.