Decent optimizations for CssAttributeCollection

[patrikwlund]

Changes

The core change is that we don't try to be a dictionary anymore, just a simple list. No need for the CssValue struct either, just store the CssAttribute directly in the list. The order of the list is the same as the attribute order, so no need to sort it every time we want to iterate over it.

Because this is a public type, these are probably considered breaking changes.

Realistic benchmark of MoveCssInline()

One invocation of MoveCssInline()
Original: 1.2ms 592kB
After: 1.0ms 482kB

[martinnormark]

Thanks for the PR!

Do you have the example CSS you used for benchmarking? I'm curious to see how performance scales with attribute key/style lookups.

[patrikwlund]

Hi @martinnormark, I created another PR with a benchmark that can be used to bench this #323

Original

Method	Mean	Error	StdDev	Median	Gen0	Allocated
AngleSharpBaseline	170.6 us	6.79 us	20.03 us	164.9 us	-	138.67 KB
MoveCssInline	832.4 us	5.43 us	14.69 us	830.9 us	30.0000	621.52 KB

After this PR

Method	Mean	Error	StdDev	Median	Gen0	Allocated
AngleSharpBaseline	174.3 us	9.63 us	28.40 us	162.9 us	-	138.67 KB
MoveCssInline	704.5 us	2.73 us	7.33 us	703.8 us	30.0000	506.61 KB

[martinnormark]

Great improvement! I might expand on the benchmarking with more automation and more example email HTML, to focus on performance of internals like this.