Implementation of DuckDBClientFactory

[Seddryck]

Goal is to support database abstraction by the means of DbProviderFactories.RegisterFactory(...)

[Seddryck]

Close #67

[coveralls]

Pull Request Test Coverage Report for Build 4588536725

• 6 of 16 (37.5%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.7%) to 85.474%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
DuckDB.NET.Data/DuckDBConnection.cs	0	3	0.0%
DuckDB.NET.Data/DuckDBClientFactory.cs	3	10	30.0%
<!--	Total:	6	16	37.5%	-->

Totals
Change from base Build 4330564513:	-0.7%
Covered Lines:	673
Relevant Lines:	784

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💛 - Coveralls