Drop floating point noise in color values

[alexykot]

This drops the floating point long trails of meaningless dust values in serialised color values.

I've opted to hardcode it to 3 decimal points because this should fully cover resolution provided by color.Color integer values. So no higher precision is necessary here, and this threshold is unlikely to ever change.

This only affects color values since those have well known precision, limited by RGBA data structure. No other values affected.

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This actually doesn't affect my case, because draco transcoder already takes care of it, and even without it the difference is not huge. But it was also very easy to do, so I've dropped this one in.

It didn't need JSON serialisation override, JSON is smart enough to not output trailing zeros, so correct rounding was enough here.

[EliCDavis]

Oh man it was that easy huh. Man I was afraid I was going to have to create a special datatype that overrides how it get's serialized to JSON.

Thanks for this!