Fix mempool.get_info, testmempoolaccept and outpoint.subscribe with the Palladium daemon

- mempool.get_info: the daemon has no incrementalrelayfee in getmempoolinfo,
  read incrementalfee from getnetworkinfo
- testmempoolaccept: the daemon does not report wtxid
- outpoint.subscribe: refuse the subscription (Coin.DAEMON_HAS_TXO_SPENDER_INDEX)
  instead of closing the session at the next block, when the daemon errors

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

README.md

@@ -91,8 +91,8 @@ When merging upstream, resolve modify/delete conflicts on these files by keeping
   bech32m for taproot) are only read by the local `electrumx_rpc query` command.
 - Palladium Core has no `getindexinfo`, `txospenderindex` (`gettxspendingprevout`) or `submitpackage` RPCs,
   so the daemon version/index checks are disabled for `COIN=Palladium`, and
-  `blockchain.outpoint.subscribe` and `blockchain.transaction.broadcast_package` return a daemon
-  error to clients.
+  `blockchain.outpoint.subscribe` is refused with an explicit error (`Coin.DAEMON_HAS_TXO_SPENDER_INDEX`)
+  and `blockchain.transaction.broadcast_package` returns the daemon error to clients.
 - The daemon must run with `txindex=1`.
 - Same genesis blocks as Bitcoin (mainnet, testnet3, regtest), 80-byte headers, sha256d PoW.
 - Parameters (address prefixes, ports, genesis hashes) were taken from the Palladium Core chain parameters.