Initial QSfera import

Server/vendor/github.com/cenkalti/backoff/v5/README.md

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+# Exponential Backoff [![GoDoc][godoc image]][godoc]
+
+This is a Go port of the exponential backoff algorithm from [Google's HTTP Client Library for Java][google-http-java-client].
+
+[Exponential backoff][exponential backoff wiki]
+is an algorithm that uses feedback to multiplicatively decrease the rate of some process,
+in order to gradually find an acceptable rate.
+The retries exponentially increase and stop increasing when a certain threshold is met.
+
+## Usage
+
+Import path is `github.com/cenkalti/backoff/v5`. Please note the version part at the end.
+
+For most cases, use `Retry` function. See [example_test.go][example] for an example.
+
+If you have specific needs, copy `Retry` function (from [retry.go][retry-src]) into your code and modify it as needed.
+
+## Contributing
+
+* I would like to keep this library as small as possible.
+* Please don't send a PR without opening an issue and discussing it first.
+* If proposed change is not a common use case, I will probably not accept it.
+
+[godoc]: https://pkg.go.dev/github.com/cenkalti/backoff/v5
+[godoc image]: https://godoc.org/github.com/cenkalti/backoff?status.png
+
+[google-http-java-client]: https://github.com/google/google-http-java-client/blob/da1aa993e90285ec18579f1553339b00e19b3ab5/google-http-client/src/main/java/com/google/api/client/util/ExponentialBackOff.java
+[exponential backoff wiki]: http://en.wikipedia.org/wiki/Exponential_backoff
+
+[retry-src]: https://github.com/cenkalti/backoff/blob/v5/retry.go
+[example]: https://github.com/cenkalti/backoff/blob/v5/example_test.go