during untar, read ahead, causing decompression to occur in the bg (#18205)

* shared buffered decompressor for untar

* spell check in comment

runtime/src/lib.rs

@@ -34,6 +34,7 @@ mod read_only_accounts_cache;
 pub mod rent_collector;
 pub mod secondary_index;
 pub mod serde_snapshot;
+mod shared_buffer_reader;
 pub mod snapshot_config;
 pub mod snapshot_package;
 pub mod snapshot_runtime_info;
@@ -46,6 +47,7 @@ mod system_instruction_processor;
 pub mod transaction_batch;
 pub mod vote_account;
 pub mod vote_sender_types;
+pub mod waitable_condvar;
 
 #[macro_use]
 extern crate solana_metrics;