fix: add backward compatibility for MCP servers returning older protocol versions

- Add ProtocolVersions interface with version constants
- Change protocolVersion() to protocolVersions() returning List<String>
- Streamable HTTP clients now support both 2024-11-05 and 2025-03-26
- Fixes compatibility with MCP servers that return 2024-11-05 instead of 2025-03-26

Resolves #436
Related to #438

Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>