mempool: honor reduced-data grandfathering when relaying spends

[kwsantiago]

Reduced-data (RDTS) exempts inputs spending UTXOs created before activation from the reduced-data rules. Consensus applies this per-input in ConnectBlock (validation.cpp), but the mempool script checks do not: PolicyScriptChecks and ConsensusScriptChecks apply the reduced-data flags uniformly to every input. As a result a spend of a grandfathered UTXO is valid in a block but rejected as non-standard at relay, so Knots nodes won't propagate it.

This strips the reduced-data flags for inputs spending pre-activation UTXOs in both mempool script checks, using the per-input flags that CheckInputScripts already supports and mirroring ConnectBlock. Pre-activation behavior is unchanged (nothing is exempted, the relay filter still applies).

Test: feature_reduced_data_utxo_height.py gains a mempool case, a spend of a grandfathered OP_IF-tapscript UTXO is relayable, while a newly-created one is still rejected. (OP_IF-in-tapscript is used rather than an oversized push because the latter is masked by the unrelated 80-byte witness-stack-item standardness rule.)

[luke-jr]

The current behaviour is intentional

[kwsantiago]

Agreed, the policy rejection is intentional (a grandfathered spend's change output typically reuses the same script). Closing this. I'll follow up with a way for miners to manually override the rejection instead, as you suggested.