Do not throw NotSupportedException in DuckDBCommand.Prepare

[roee88]

Closes #118

[coveralls]

Pull Request Test Coverage Report for Build 5499460466

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 86.447%

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Totals
Change from base Build 5495294166:	0.0%
Covered Lines:	765
Relevant Lines:	881

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💛 - Coveralls