switch to case-insensitive http header comparisons, also fix racing in linux.jai

[DaseinPhaos]

Thanks for the awesome package!

This PR fixes a tiny issue wrt http header comparisons. According to the mdn reference:

An HTTP header consists of its case-insensitive name followed by a colon...

But the previous parsing code used hard-coded literals when parsing specific headers, resulting in some requests not being correctly parsed. This PR fixes that.