introduce checkpointer (#1538)

* introduce checkpointer

* implement PerformCheckpoint for WalRegistry

* fmt

Author: MarinPostma

libsql-wal/Cargo.toml

@@ -46,6 +46,7 @@ s3s-fs = { git = "https://github.com/Nugine/s3s" }
 s3s-aws = { git = "https://github.com/Nugine/s3s" }
 tracing-subscriber = "0.3"
 aws-credential-types = { version = "1", features = ["test-util"] }
+tokio = { version = "*", features = ["test-util"] }
 
 [[bench]]
 name = "benchmarks"