Migrate CI to use GitHub Actions.
### Motivation:
To migrate to GitHub actions and centralised infrastructure.
### Modifications:
Changes of note:
* Adopt swift-format using rules from SwiftNIO.
* Remove scripts and docker files which are no longer needed.
* Disabled warnings-as-errors on Swift 6.0 CI pipelines for now.
### Result:
Feature parity with old CI.
Motivation:
We would like to make this work for Musl so that we can build fully
statically linked binaries that use AsyncHTTPClient.
Modifications:
Define `_GNU_SOURCE` as a compiler argument; doing it in a source file
doesn't work properly with modular headers.
Add imports of `Musl` in appropriate places.
`Musl` doesn't have `strptime_l`, so avoid using that.
Result:
async-http-client will build for Musl.
Motivation:
If we backoff sufficiently far we can overflow Int64, which will cause
us to crash.
Modifications:
Clamp the backoff value before we convert to Int64.
Results:
No crashes!
Marc Prud'hommeauxandGitHub
Rick Newton-RogersandGitHub
Alastair HoughtonandGitHub
David NadobaandGitHub
Cory BenfieldandGitHub