Merge bitcoin/bitcoin#30817: test: Add coverage for dumptxoutset failure robustness

c2b779da4e refactor: Manage dumptxoutset RAII classes with std::optional (Fabian Jahr)
4b5bf335ad test: Add coverage for failing dumptxoutset behavior (Fabian Jahr)

Pull request description:

  This adds a test that checks that network activity is not suspended if dumptxoutset fails in the middle of its process which is implemented with the `NetworkDisable` RAII class. I would have liked to add coverage for the `TemporaryRollback` RAII class but that seems a lot more tricky since the failure needs to happen at some point after the rollback and on the scale of our test chain here I couldn't find a way to do it yet. This was requested by pablomartin4btc here: https://github.com/bitcoin/bitcoin/pull/30808#pullrequestreview-2280450117. To test the test you can comment out the content of the destructor of `NetworkDisable`.

  It also addresses the feedback by ryanofsky to use `std::optional` instead of `std::unique_ptr` for the management of the RAII object: https://github.com/bitcoin/bitcoin/pull/30808#discussion_r1744149228

ACKs for top commit:
  achow101:
    ACK c2b779da4e
  pablomartin4btc:
    cr & tACK c2b779da4e
  tdb3:
    ACK c2b779da4e
  BrandonOdiwuor:
    Code Review ACK c2b779da4e
  theStack:
    ACK c2b779da4e

Tree-SHA512: 9556e75014a2599bb870b70faf887608b332f2312626333f771d4ec11c04f863a2cf17e223ec473d4e8b0c9e8008394a4e0c321561f7ef3a2eec713dcfaea58a

test/functional/rpc_dumptxoutset.py

@@ -28,7 +28,7 @@ class DumptxoutsetTest(BitcoinTestFramework):
 
         FILENAME = 'txoutset.dat'
         out = node.dumptxoutset(FILENAME, "latest")
-        expected_path = node.datadir_path / self.chain / FILENAME
+        expected_path = node.chain_path / FILENAME
 
         assert expected_path.is_file()
 
@@ -60,6 +60,16 @@ class DumptxoutsetTest(BitcoinTestFramework):
         assert_raises_rpc_error(
             -8, 'Invalid snapshot type "bogus" specified. Please specify "rollback" or "latest"', node.dumptxoutset, 'utxos.dat', "bogus")
 
+        self.log.info(f"Test that dumptxoutset failure does not leave the network activity suspended")
+        rev_file = node.blocks_path / "rev00000.dat"
+        bogus_file = node.blocks_path / "bogus.dat"
+        rev_file.rename(bogus_file)
+        assert_raises_rpc_error(
+            -1, 'Could not roll back to requested height.', node.dumptxoutset, 'utxos.dat', rollback=99)
+        assert_equal(node.getnetworkinfo()['networkactive'], True)
+
+        # Cleanup
+        bogus_file.rename(rev_file)
 
 if __name__ == '__main__':
     DumptxoutsetTest(__file__).main()