refactor: Simplify nonce management by replacing global cache with direct fetch

Remove NonceCache singleton pattern and replace with fetch_nonce_info function
that directly fetches nonce information from RPC. This simplifies the API by
eliminating cache initialization and state management, making it easier for
users to manage durable nonces.

examples/nonce_cache/src/main.rs

@@ -1,10 +1,12 @@
-use std::sync::{
-    atomic::{AtomicBool, Ordering},
-    Arc,
+use std::{
+    str::FromStr,
+    sync::{
+        atomic::{AtomicBool, Ordering},
+        Arc,
+    },
 };
 
-use sol_trade_sdk::common::nonce_cache::NonceCache;
-use sol_trade_sdk::common::TradeConfig;
+use sol_trade_sdk::common::{nonce_cache::fetch_nonce_info, TradeConfig};
 use sol_trade_sdk::TradeTokenType;
 use sol_trade_sdk::{
     common::AnyResult,
@@ -13,7 +15,7 @@ use sol_trade_sdk::{
     SolanaTrade,
 };
 use solana_commitment_config::CommitmentConfig;
-use solana_sdk::signature::Keypair;
+use solana_sdk::{pubkey::Pubkey, signature::Keypair};
 use solana_streamer_sdk::match_event;
 use solana_streamer_sdk::streaming::event_parser::common::filter::EventTypeFilter;
 use solana_streamer_sdk::streaming::event_parser::common::EventType;
@@ -121,10 +123,8 @@ async fn pumpfun_copy_trade_with_grpc(trade_info: PumpFunTradeEvent) -> AnyResul
     let recent_blockhash = client.rpc.get_latest_blockhash().await?;
 
     // Setup nonce cache
-    let nonce_account_str = "use_your_nonce_account_here";
-    NonceCache::get_instance().init(Some(nonce_account_str.to_string()));
-    NonceCache::get_instance().fetch_nonce_info_use_rpc(&client.rpc).await?;
-    let durable_nonce = NonceCache::get_durable_nonce_info();
+    let nonce_account_str = Pubkey::from_str("use_your_nonce_account_here")?;
+    let durable_nonce = fetch_nonce_info(&client.rpc, nonce_account_str).await;
 
     // Buy tokens
     println!("Buying tokens from PumpFun...");
@@ -154,7 +154,7 @@ async fn pumpfun_copy_trade_with_grpc(trade_info: PumpFunTradeEvent) -> AnyResul
         close_input_token_ata: false,
         create_mint_ata: true,
         open_seed_optimize: false,
-        durable_nonce: Some(durable_nonce),
+        durable_nonce: durable_nonce,
         fixed_output_token_amount: None,
     };
     client.buy(buy_params).await?;