Compress middleware: matchAcceptEncoding uses substring match and ignores q=0

Description

The matchAcceptEncoding function in middleware/compress.go uses strings.Contains to match encoding names in the Accept-Encoding header. This has two problems:

1. Substring matching produces false positives

func matchAcceptEncoding(accepted []string, encoding string) bool {
	for _, v := range accepted {
		if strings.Contains(v, encoding) {   // substring match, not exact
			return true
		}
	}
	return false
}

For example:

• Accept-Encoding: br incorrectly matches encoding b (since "br" contains "b")
• Accept-Encoding: bgzip incorrectly matches encoding gzip

2. Quality value q=0 is ignored

Per RFC 9110 Section 12.5.3, a quality value of q=0 means the encoding is not acceptable. But strings.Contains("gzip;q=0", "gzip") returns true, so the middleware will compress with gzip even when the client explicitly rejects it.

Reproduction

// These all incorrectly return true:
matchAcceptEncoding([]string{"gzip;q=0"}, "gzip")   // should be false (q=0 = not acceptable)
matchAcceptEncoding([]string{"br"}, "b")             // should be false (not exact match)
matchAcceptEncoding([]string{"bgzip"}, "gzip")       // should be false (not exact match)

Fix

Parse the encoding name properly by splitting on ; to separate quality parameters, trimming whitespace, performing exact string comparison, and rejecting q=0.