…ions (1/3) (near#15904)

First of a 3-PR stack adding gas-key support to meta transactions via a
new `Action::DelegateV2`. Replaces the extension-based stack (near#15883,
near#15884, near#15885) with the versioned design suggested in review there.

Adds the wire types and the nesting guard, but no execution yet:
validation rejects `DelegateV2` (`UnsupportedProtocolFeature`) and the
apply path fails it gracefully. Execution lands in the next PR in the
stack.

Design:
- `DelegateActionV2` mirrors `TransactionV1`: its `nonce:
TransactionNonce` selects either the access key nonce or one of a gas
key's parallel nonces by index.
- `VersionedDelegateActionPayload` (wire enum, currently just `V2`) is
the signed payload of `VersionedSignedDelegateAction`. Future versions
add a variant here instead of a new `Action` variant, so the delegate
nesting guard stays frozen, and the variant byte is covered by the
signature so versions cannot be confused.
- `DelegateV2` signs under its own NEP-461 discriminant (NEP-611, gas
keys), making V1 and V2 signing domains disjoint by construction.
- `VersionedDelegateActionRef`/`VersionedSignedDelegateActionRef` are
borrowing wrappers for code handling V1 and V2 uniformly (the
`VersionedActionReceipt` pattern).
- A dedicated `ProtocolFeature::DelegateV2` (protocol version 85) gates
the action independently of `ProtocolFeature::GasKeys`, so it can be
pulled from the release on its own if needed.

Includes `ActionView::DelegateV2`, cost/fee handling, and trivial match
arms across the workspace.

Protocol schema and openapi specs (1.2.11) are regenerated.