feat(css-parser): CSS Parser: namespace at rule

[denbezrukov]

Summary

namespace at rule.

https://developer.mozilla.org/en-US/docs/Web/CSS/@namespace#specifications

@namespace <namespace-prefix>? [ <string> | <url>] ;

Test Plan

cargo test

[netlify]

✅ Deploy Preview for biomejs canceled.

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🔨 Latest commit	08202d4
🔍 Latest deploy log	https://app.netlify.com/sites/biomejs/deploys/659c2fd9ca67b60008070d3b

[github-actions]

Parser conformance results on

js/262

Test result	main count	This PR count	Difference
Total	49701	49701	0
Passed	48721	48721	0
Failed	980	980	0
Panics	0	0	0
Coverage	98.03%	98.03%	0.00%

jsx/babel

Test result	main count	This PR count	Difference
Total	40	40	0
Passed	37	37	0
Failed	3	3	0
Panics	0	0	0
Coverage	92.50%	92.50%	0.00%

symbols/microsoft

Test result	main count	This PR count	Difference
Total	6322	6322	0
Passed	2036	2036	0
Failed	4286	4286	0
Panics	0	0	0
Coverage	32.20%	32.20%	0.00%

ts/babel

Test result	main count	This PR count	Difference
Total	662	662	0
Passed	592	592	0
Failed	70	70	0
Panics	0	0	0
Coverage	89.43%	89.43%	0.00%

ts/microsoft

Test result	main count	This PR count	Difference
Total	17646	17646	0
Passed	13452	13452	0
Failed	4192	4192	0
Panics	2	2	0
Coverage	76.23%	76.23%	0.00%

[codspeed-hq]

CodSpeed Performance Report

Merging #1472 will degrade performances by 21.82%

_{⚠️ No base runs were found}

_{Falling back to comparing feat/css-namespace (08202d4) with main (c1fdabc)}

Summary

❌ 1 regressions
✅ 92 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	main	feat/css-namespace	Change
❌	big5-added.json[uncached]	2.9 ms	3.7 ms	-21.82%

[faultyserver]

I'm hoping to figure out how to differentiate "function tokens" from identifiers soon, which the CSS spec defines as just <ident>( with no spaces in between. It'll most likely be the same way that CSS_DIMENSION_VALUE works now, where the lexer returns a special kind that can be converted to the actual kind (in this case, IDENT).

I'd thought about making the parser not skip over whitespace, but i think that just makes all of the steps in the parser more complicated, while re-casting a token to a different kind is effectively free and makes checks incredibly fast, too.

[denbezrukov]

I agree, having function_tokens would be better.

[faultyserver]

I can go ahead and get started on that. I've got a good idea in mind already.