Masked text animator drifts a pixel per loop on ldpi

The brief

Lottie's masked text animator accumulates a one-pixel rounding drift every loop on ldpi screens, visibly walking subtitles across long animations.

Acceptance criteria

• Looping masked text holds pixel-identical position after 100 loops
• No regression in existing animation snapshot baselines
• Fix covered by an ldpi robolectric screenshot test
• Changelog entry included