Function splitSetCookieHeaders

Split a raw Set-Cookie header value (or collapsed multi-value string) into individual cookie strings.

This is non-trivial because:

• Expires values contain commas: "Expires=Thu, 01 Jan 2099 00:00:00 GMT"
• Multiple Set-Cookie headers may be collapsed with ", " by some HTTP stacks

Strategy: Token-based state machine that properly handles:

• Quoted values with commas inside (e.g., foo="bar,baz")
• Escaped quotes inside quoted values (e.g., foo="bar\"baz")
• Attribute values that may contain commas
• Only commits a cookie when we've seen both name and value