Add style property transitions

[Zoxc]

This add style property transitions which can be used by the transition method on Style. For example: transition(Background, Transition::linear(0.1)). Users of prop_extracter! will get these animations applied if the property type supports them (current f64 and Color).

The themes example is updated to use them.

[codecov]

Codecov Report

Merging #143 (1264f0f) into main (d10a3c2) will decrease coverage by 0.08%.
The diff coverage is 0.37%.

@@           Coverage Diff            @@
##            main    #143      +/-   ##
========================================
- Coverage   5.09%   5.02%   -0.08%     
========================================
  Files         56      56              
  Lines      11087   11268     +181     
========================================
+ Hits         565     566       +1     
- Misses     10522   10702     +180     

Files	Coverage Δ
src/views/scroll.rs	0.00% <0.00%> (ø)
src/context.rs	0.00% <0.00%> (ø)
src/window_handle.rs	0.00% <0.00%> (ø)
src/view.rs	0.00% <0.00%> (ø)
src/inspector.rs	0.00% <0.00%> (ø)
src/style.rs	11.78% <0.63%> (-1.38%)	⬇️

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