[Feature Request]Adding compatibility support for KingbaseES

Hi asyncpg maintainers,

  I am writing to propose adding support for KingbaseES, a widely used database in China that is highly compatible with the PostgreSQL wire protocol. I plan to contribute and maintain this adaptation over the next 2 months.

 To ensure the performance and stability of asyncpg remain unaffected, I will follow these principles:
 1.Non-Invasive Implementation: I will not modify the Cython-based protocol parser (asyncpg/protocol/). The changes will be isolated to Authentication tweaks and Type Introspection SQL adjustments (handling minor pg_catalog differences).
 2.Strict Testing: I will run the full asyncpg test suite against KingbaseES and add dedicated integration tests for any variant-specific edge cases.
 3.Maintenance Commitment: I fully understand the burden of supporting variants. I commit to taking long-term ownership of Kingbase-related issues to keep the driver up-to-date.

 I have already verified basic connections locally. Would the community be open to accepting a Pull Request for this? Also, do you prefer handling such variants via automatic detection (server version) or explicit connection flags?
 Thank you for your incredible work on this high-performance driver!

Inizia esaminando asyncpg/protocol/ e i percorsi SQL esistenti per Authentication e Type Introspection, per identificare le assunzioni di PostgreSQL rilevanti per KingbaseES. Confronta questi percorsi con le differenze segnalate in pg_catalog e decidi se sia appropriato il rilevamento della versione del server o un flag di connessione esplicito. Il lavoro è completato quando le connessioni di base funzionano, i test di integrazione specifici della variante passano e l’intera suite di test di asyncpg rimane stabile con KingbaseES.