Remove radio-group transition lag from Customizer controls

[georgeolaru]

Summary

The shared sm_radio control still feels slow to click even when the underlying setting updates quickly.

Root cause

The common radio-group label styling uses a 300ms transition in src/_js/customizer/scss/controls/_radio-group.scss, so every state change animates background, color, and border updates. That adds cosmetic lag to controls like Voice Tuner and Font Sizing even when the checked state itself flips immediately.

Scope

Remove the shared label transition for .sm-radio-group controls, rebuild the Customizer bundle, and verify the interaction feel in both Voice Tuner and Font Sizing.

[georgeolaru]

Verified the no-transition experiment after rebuilding the Customizer bundle.

Shared radio-group labels now resolve to transition-duration: 0s in the live Customizer for both:

• sm_voice_formality (Voice Tuner)
• sm_font_sizing (Font Sizing)

That removes the old 300ms cosmetic animation from the common sm_radio control while leaving the underlying setting behavior unchanged.

Added a small regression test in tests/js/radio-group-style.test.js so the shared sm-radio-group label rule fails if a transition declaration is reintroduced.