refactor: code and remove unused imports

- change `std::collections::btreeset` to `btreeset::new()` in line 19
- remove unused imports

mithril-common/src/chain_observer/pallas_observer.rs

@@ -15,7 +15,10 @@ use pallas_network::{
 };
 
 use pallas_primitives::ToCanonicalJson;
-use std::path::{Path, PathBuf};
+use std::{
+    collections::BTreeSet,
+    path::{Path, PathBuf},
+};
 
 use crate::chain_observer::interface::*;
 use crate::chain_observer::{ChainAddress, TxDatum};
@@ -194,7 +197,7 @@ impl PallasChainObserver {
             .map_err(|err| anyhow!(err))
             .with_context(|| "PallasChainObserver failed to get current era")?;
 
-        let state_snapshot = queries_v16::get_stake_snapshots(statequery, era, vec![])
+        let state_snapshot = queries_v16::get_stake_snapshots(statequery, era, BTreeSet::new())
             .await
             .map_err(|err| anyhow!(err))
             .with_context(|| "PallasChainObserver failed to get stake snapshot")?;