72db4accbf coins: drop stale cursor null checks (Lőrinc)
3d2f2d8de0 coins: pass UTXO stats view by reference (Lőrinc)
35aedb2823 coins: drop cursor from base view (Lőrinc)
c6fbe2f66c coins: pass DB view to cursor users (Lőrinc)
Pull request description:
**Problem:** `CCoinsView::Cursor()` makes cursor iteration look like a generic coins view operation, but cursor iteration is only supported by the DB-backed coins view.
The cache override only threw, and the `coins_view` fuzz target only asserted that deterministic unsupported throw path.
**Fix:** Make cursor iteration a `CCoinsViewDB` operation.
Cursor users now take the DB-backed view directly, `CCoinsView` no longer exposes `Cursor()`, and the fuzz target keeps DB-backed cursor coverage while dropping the unsupported cache throw probe.
The UTXO stats path is also tightened to pass the non-null DB view by reference, and stale null handling for DB cursors is removed.
This was extracted from review discussion in https://github.com/bitcoin/bitcoin/pull/35295#discussion_r3420576781 and extended based on https://github.com/bitcoin/bitcoin/pull/35562#issuecomment-4746585893.
ACKs for top commit:
achow101:
ACK 72db4accbf
sedited:
Re-ACK 72db4accbf
w0xlt:
ACK 72db4accbf
andrewtoth:
ACK 72db4accbf
Tree-SHA512: 12a81330a6ec1b91a7e4393f3761ea9ed4702ecb24312f1defa5a9a079a396ce921fc52f74fe296e5ac7ab20d5b5a8a84e858c96847f333c58b7fa9de9e8143e
773b1c9aa5