fix(pxe): only skip sync for stub overrides, not on-chain class overrides

[dbanks12]

Summary

PXE skips sync for any contract that appears in SimulationOverrides.contracts. The skip was added to defend against a hostile no-op sync_state in account stubs (simulated_*_account_contract); without it, sync would trigger their assert(false). The blanket skip is too coarse: it also blocks pre-existing notes from being loaded for real contract overrides (e.g. fastForwardContractUpdate), causing private calls that read prior state to fail with "Failed to get a note".

Fix

Narrow the skip to overrides whose class id isn't published on chain. On-chain classes have full artifacts and need sync (upgrade-sim flow). Off-chain-only classes (account stubs registered via pxe.registerContractClass) keep being skipped — the existing behavior they need.

Test plan

• e2e_kernelless_simulation (account stub overrides): 7/7 pass
• e2e_contract_updates (upgrade-sim via fastForwardContractUpdate, including the new private-dispatch test upstack): 6/6 pass

[dbanks12]

• fix(pxe): only skip sync for stub overrides, not on-chain class overrides #23016 👈 (View in Graphite)
• feat: expose wallet.registerContractClass (prep for simulating contract upgrades) #22932 : 3 other dependent PRs (#22833 , #23045 , #23054 )
• feat: public data tree overrides for simulation #22830
• refactor: drop artifact field from SimulationOverrides #22957
• merge-train/fairies

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