1.28.1-prerelease

Changes

• Add a public ForceFlushAsync API on the Tracer (#1599)
• CIApp: Update Bitrise spec (#1593)

Fixes

• Fix memory leak in native code (#1564, #1600)

Build / Test

• Switch to Nuke consolidated pipeline (#1595, #1587, #1598)
• Add a custom test framework to monitor execution of unit tests (#1572)

Changes since 1.28.0