preserve cookie options when re-signing with rotated keys

[raashish1601]

What changed

• Rework signed-cookie handling so generated .sig values carry serialized options (path/domain/maxAge/expires/etc) with an options signature.
• On get/refresh path, verify and reuse those options when re-signing with a newer key, so attributes are preserved.
• Add regression test for persistent cookie attribute retention after key rotation.
• Update express tests for .sig cookie content format changes.