Npgsql: Use Npgsql.CrateDB instead of vanilla Npgsql

[amotl]

About

Probing better type support for Npgsql, or even trying to build it.

Status

I don't know why dotnet test succeeds test runs in conditions I would expect it to fail. Anyway, on .NET 8, it just errors out like

    /path/to/cratedb-examples/by-language/csharp-npgsql/tests/DemoProgramTest.cs(25): error TESTERROR:
      demo.tests.DemoProgramTest.TestSystemQueryExample (1ms): Error Message: Class fixture type 'demo.tests.DatabaseFixture' threw in its constructor
      ---- Npgsql.NpgsqlException : Unknown message code: 0

Npgsql.CrateDB is outdated, as expected, and we need to investigate if it would yield a positive outcome if it would be resurrected.

[amotl]

Closing this in favor of GH-777: Npgsql 8.x and 9.0 provide good support for mapping CrateDB's special data types to relevant types in .NET/Npgsql.