LottieConfiguration shared instance in Swift 6

[prengifo]

Which Version of Lottie are you using?

Lottie 4.5.0

Problem

While enabling complete concurrency checks for Swift 5 in Xcode 16, we get a warning that accessing the shared instance from LottieConfiguration is not concurrency-safe. This should be tagged correctly with some concurrency strategy to avoid the warning.

LottieConfiguration.shared.renderingEngine = .mainThread

Expected Behavior

No warning should be raised by the compiler

Actual Behavior

A warning is raised in Swift 5 with complete concurrency check, while an error will be raised in Swift 6.

[calda]

Static mutable globals like this are never concurrency-safe.

Making Lottie compatible with Swift 6 mode and strict concurrency checking will require probably require breaking API changes.