fix: default to drawHierarchy rendering when available

[ajkolean]

Resolves rendering issues (#606, #790) caused by layer.render(in:) no longer matching runtime visuals on iOS 17+. This change uses drawHierarchyInKeyWindow: true when safe (e.g. SwiftUI + key window), preserving CI stability while improving snapshot fidelity.

[mattmapadmi]

We've found with drawInHierarchy we get very unstable tests. Some of it is changes we need to make (like disabling cross-fade animations), but then there's lots of really odd single-pixel changes.

We're using ScreenshotBot for diffs, which by default doesn't have any leniency for miniscule changes.

We'll switch the rendering mode to .disabled and accept our rounded rectangles will be wrong (#606), but this PR might be a surprise for some consumers of the library.