fix: ignore invalid accept-language weights

[rubas]

Summary

This fixes how Localize.AcceptLanguage treats HTTP q-values.

RFC 9110 defines Accept-Language entries as language ranges with an optional quality weight. Those weights are q-values from 0 to 1, where 0 means "not acceptable" and an omitted q-value means 1.

With this change:

• fr;q=0,en;q=0.5 selects en, not fr.
• fr;q=0,en;q=0 returns no match.
• en;q=2,fr;q=1 selects fr, because q=2 is outside the valid q-value range.
• malformed q-values are ignored instead of being treated like an omitted q-value.
• entries without a q-value still default to 1.0.

References:

• RFC 9110 Section 12.5.4, Accept-Language: https://datatracker.ietf.org/doc/html/rfc9110#section-12.5.4
• RFC 9110 Section 12.4.2, Quality Values: https://datatracker.ietf.org/doc/html/rfc9110#section-12.4.2