refactor(backend): migrate from backoff to backon (#356)

Hello,

Removed the unmaintained  `backoff` crate in the `rustic_backend` crate.
Replaced it with the relatively similar `backon` crate.

If `backon` as simpler API, it also lacks a few features that `backoff`
had.
For instance: `no_max_delay` or `backoff::retry_notify`. 
To make up for it:
- I opened Xuanwo/backon#160 on the `backon`
github.
- I implemented an internal module `backon_extension` inside
`backend::rest`.

Let me know what you think of the code!

Fixes #351

---------

Co-authored-by: Alexander Weiss <[email protected]>
Co-authored-by: simonsan <[email protected]>

crates/backend/Cargo.toml

@@ -42,7 +42,7 @@ opendal = [
   "tokio/rt-multi-thread",
   "dep:typed-path",
 ]
-rest = ["dep:reqwest", "dep:backoff"]
+rest = ["dep:reqwest", "dep:backon"]
 rclone = ["rest", "dep:rand", "dep:semver"]
 
 [dependencies]
@@ -78,7 +78,7 @@ aho-corasick = { workspace = true }
 walkdir = "2.5.0"
 
 # rest backend
-backoff = { version = "0.4.0", optional = true }
+backon = { version = "1.2.0", optional = true }
 reqwest = { version = "0.12.8", default-features = false, features = ["json", "rustls-tls-native-roots", "stream", "blocking"], optional = true }
 
 # rclone backend