Raise bitcoind polling interval (#19)

MutinyNet's much longer chain history makes the wallet's mempool
handling noticeably more expensive. Recent work moved that work off the
async executor to improve the runtime performance but a single poll can still
consume nearly the full 2 second interval creating constant CPU pressure.

Raise the interval to 10 seconds as a temporary mitigation. It reduces
steady background CPU load without changing the underlying behavior,
and buys time until the BDK performance issue is fixed.

Author: amackillop

src/chain/bitcoind.rs

@@ -41,7 +41,7 @@ use crate::logger::{log_bytes, log_error, log_info, log_trace, LdkLogger, Logger
 use crate::types::{ChainMonitor, ChannelManager, DynStore, Sweeper, Wallet};
 use crate::{Error, NodeMetrics};
 
-const CHAIN_POLLING_INTERVAL_SECS: u64 = 2;
+const CHAIN_POLLING_INTERVAL_SECS: u64 = 10;
 const CHAIN_POLLING_TIMEOUT_SECS: u64 = 10;
 
 pub(super) struct BitcoindChainSource {