feat: [#2335] Add current playback time & playback rate

[eonarheim]

===:clipboard: PR Checklist :clipboard:===

• 📌 issue exists in github for these changes
• 🔬 existing tests still pass
• 🙈 code conforms to the style guide
• 📐 new tests written and passing / old tests updated with new scenario(s)
• 📄 changelog entry added (or not needed)

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Closes #2335

This PR adds a new method onto ex.Sound.getCurrentTime() to get the current playback time into the currently playing track.

Additionally this PR adds the current playback rate that can be get/set on ex.Sound.playbackRate, 1.0 is the default playback rate, 2.0 is twice the speed, and 0.5 is half speed.