fix: trim OWS after commas when splitting list parameters

[stareezy-1]

Summary

Fixes #1084

Problem

parseInto splits list-style header/query params on a literal comma:

values = strings.Split(value, ",")

RFC 9110 §5.6.1 list grammar permits optional whitespace (OWS) around each comma, so a conventional If-None-Match: "a", "b" produces ["\"a\"", " \"b\""] — every element after the first keeps a leading space. conditional.trimETag strips quotes but not whitespace, so the space-tainted element can never equal a bare ETag: a 304-eligible request silently returns a full 200.

Reproduction:

If-None-Match: "target-tag"          → 304 (correct)
If-None-Match: "other-tag","target-tag" → 304 (correct)
If-None-Match: "other-tag", "target-tag" → 200 (bug)

Fix

Trim OWS (" \t") from each element at the shared split site in parseInto. This fixes every list-style header/query param at once rather than just the conditional package, matching the fix location suggested in the issue.

Tests

TestIfNoneMatchOWSAfterComma in conditional/params_test.go registers a real operation with embedded Params and asserts:

Case	Verifies
"other-tag", "target-tag" (OWS on second element)	304 — fails without the fix
"target-tag", "other-tag" (OWS elsewhere)	304
"other-tag","target-tag" (no space)	304
non-matching list	200

All existing tests continue to pass (go test -race ./...).