refactor: optimize remove duplicated properties

[vladitasev]

When the removeDuplicatedValues configuration setting is set to true, it is unavoidable to have two embedded loops to remove duplicates, as both the props and the values must be compared.

However, if only removeDuplicatedProperties is set to true, then duplicates can be removed with only one loop - iterate from the last node to the first, keep the first occurrence of each prop (as it will be the last in the CSS selector), and remove all others.

For large, programmatically generated selectors, most commonly :root { ... } and hundreds of CSS variables inside, this optimization can reduce the time needed by the plugin by a minute or more.

[ChristianMurphy]

Thanks @vladitasev!
Would you be able to take a look at why CI is failing with these changes?

[vladitasev]

Hey @ChristianMurphy
Of course,
It was the line length - I needed to move the 2 comments to separate lines in order to satisfy the linter. The build should be passing now.

[ChristianMurphy]

Thanks @vladitasev!
LGTM, an ideas on how to test the performance characteristics to ensure no regressions come up?