Reorder initializers to silence a warning.

[jminor]

This PR fixes a C++ compiler warning introduced in #1887. The order of the initializers in the constructors for Color and Item now match the order of the arguments so there are no unexpected side effects from the execution order.

The warnings looked like this:

/Users/jminor/git/otio-wasm/OpenTimelineIO/src/opentimelineio/item.cpp:25:7: warning: field '_enabled' will be initialized after
      field '_color' [-Wreorder-ctor]
   25 |     , _enabled(enabled)
      |       ^~~~~~~~~~~~~~~~~
      |       _color(color)
   26 |     , _color(color)
      |       ~~~~~~~~~~~~~
      |       _enabled(enabled)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.10%. Comparing base (829a913) to head (126c393).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1960   +/-   ##
=======================================
  Coverage   85.10%   85.10%           
=======================================
  Files         181      181           
  Lines       12768    12768           
  Branches     1206     1206           
=======================================
  Hits        10866    10866           
  Misses       1719     1719           
  Partials      183      183           

Flag	Coverage Δ
py-unittests	85.10% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/opentimelineio/color.cpp	96.25% <100.00%> (ø)
src/opentimelineio/item.cpp	91.86% <100.00%> (ø)

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