Implement BLOB type support

[unconverged]

We need both reading and writing of blob values.

[Giorgi]

To pass blob as parameter we need to introduce a new Enum for parameter type (DuckDBType) and use that instead of DbType

[unconverged]

Why? There is DbType.Binary value we can use here.

[Giorgi]

There is but

• DbType.Binary comment says: A variable-length stream of binary data ranging between 1 and 8,000 bytes.
• Every provider has its own DbType enum for custom types and we will need it sooner or later

There is nothing stopping us from using DbType.Binary technically but I don't know if that's the right thing to do or not.

[hazzik]

This also needs to be documented.

[Giorgi]

@hazzik Docs are in this repo: https://github.com/Giorgi/DuckDB.NET-Docs