fix(uexecutor): retain full raw_payload on inbound decode failure

[0xNilesh]

What

On an inbound payload decode failure, retain the full observed raw_payload (magic selector included) instead of the selector-stripped remainder. A successful decode still clears raw_payload (unchanged).

Why

NormalizeForTxType strips the PC20/PRC20 selector into raw_payload before decoding, then clears it on success. On a decode failure it previously left only the stripped remainder — losing the selector that determined is_pc20. That makes post-mortems hard: e.g. a failed PC20 burn stored raw_payload = "gateway-test-direct-pc20-burn" with no visible selector, so you had to dig up the original vote tx to see the 0x50433230 ("PC20") prefix.

Now the decode runs on a local, selector-stripped copy and raw_payload keeps the full original until a successful decode clears it — so a failed inbound records the exact observed bytes on-chain.

Scope / safety

• Change is confined to NormalizeForTxType in x/uexecutor/types/inbound.go; the error contract is unchanged (same decode error returned), so the keeper's VoteInbound revert path is unaffected.
• Consensus is unaffected: the inbound ballot key is hashed before normalization, on the full payload.
• Success path unchanged — raw_payload is still cleared to save storage.

Tests

Added TestNormalizeForTxType_PreservesRawPayloadOnDecodeFailure:

• PC20 decode failure → retains full original (selector included)
• PRC20 decode failure → retains full original
• un-prefixed decode failure → retains original
• PC20 success → raw_payload cleared

All existing NormalizeForTxType tests still pass; x/uexecutor/types package green.