swiftly Use swift.org API for getting releases and some snapshot toolchains

See issue #149

Using the new swift.org API is more accurate than the GitHub API, also it isn't subject to the same rate limits. Use the swift.org API instead of the GitHub API for fetching metadata about the released swift toolchains, and the newer swift branches for the snapshots.

However, there is currently no metadata for snapshots on older branches than 6.0 or main. In this case use the GitHub API to get the metadata.

Aug 08 '24 18:08 cmcgee1024

@swift-ci test macOS

Aug 09 '24 11:08 cmcgee1024

The macOS CI passes the tests, but there's the persistent environmental problem that reports an overall failure.

Test Suite 'All tests' passed at 2024-08-09 11:22:46.405.
	 Executed 67 tests, with 0 failures (0 unexpected) in 72.886 (72.895) seconds

Aug 09 '24 13:08 cmcgee1024

@swift-ci test macOS

Aug 20 '24 16:08 cmcgee1024

The macOS CI passed the xctests despite reporting an overall failure:

Test Suite 'All tests' passed at 2024-08-20 16:11:50.665.
	 Executed 67 tests, with 0 failures (0 unexpected) in 73.780 (73.789) seconds

Aug 20 '24 16:08 cmcgee1024

@patrickfreed @adam-fowler how do these latest changes look? Any remaining issues?

Aug 22 '24 11:08 cmcgee1024

@swift-ci test macOS

Aug 23 '24 12:08 cmcgee1024