…st (near#15822)

- Adds `ExecutionMetadata::V4` carrying a per-action
`Vec<AccountContract>` (one entry per action in the receipt; the
executed contract for `FunctionCall` actions, `AccountContract::None`
for everything else, ordered to match `receipt.actions`)
- Gated behind `ProtocolFeature::ExecutionMetadataV4`; pre-feature
outcomes still emit V3 with the same bytes as before
- Motivated by the need to surface the contract source for receipts
where the receiver account and the executed contract diverge — e.g.
global contracts and `UseGlobalContract` flows - so indexers / light
clients can correlate each action with its actual contract
- The first exploration of this added a `ExecutionOutcomeV1` variant on
the outcome struct itself (near#15814 introduced the versioned-enum
scaffolding, near#15816 added V1 with the byte-discriminant scheme). After
looking at it, `ExecutionMetadata` is already a borsh-native
discriminated enum, so adding `V4` there is dramatically simpler — no
custom serde tricks, no boundary constants, no struct migration across
~50 call sites.
- Splits the result types: per-action `ActionResult` carries a single
`executed_contract: AccountContract` (defaults to
`AccountContract::None`, set by `apply_action`'s `FunctionCall` arm);
receipt-level `ActionReceiptResult` owns `executed_contracts:
Vec<AccountContract>` and its `merge` appends one contract per action,
so the per-action invariant lives in one place
- `ActionReceiptResult::set_error` centralizes the failure path (record
the error, drop queued receipts / proposals / burnt balances); called
from both `merge`'s `Err` arm and the `LackBalanceForStorageStaking`
post-action storage check (which previously faked it by merging a
synthetic `ActionResult` — under the new merge that would push a stray
`AccountContract::None` onto `executed_contracts`)
- `ExecutionMetadataView` gains `contracts:
Option<Vec<AccountContract>>`, `serde(skip_serializing_if =
"Option::is_none")` so V1..V3 RPC bytes are byte-identical to before
- Closes near#14622

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Co-authored-by: Claude Opus 4.7 (1M context) <[email protected]>