2026 Winter update

Cumulative update to make library even more perfect

1. Making copyrights less annoying.
2. Added experimental cache engine base on Shared Memory Functions.
3. Serialization of string values has been excluded from Serialize cache engine.
4. Support of Link header has been added.
5. Deprecated function curl_close has been removed.

Minor improvements like improving code quality and removing unnecessary features.

Full Changelog: 2.1.1...2.2.0