Add `Decimal` support for `bind_parameter`

[PeterlitsZo]

I find there is code like:

fn bind_parameter<P: ?Sized + ToSql>(&self, param: &P, col: usize) -> Result<()> {
    let value = param.to_sql()?;

    let ptr = unsafe { self.stmt.ptr() };
    let value = match value {
        ToSqlOutput::Borrowed(v) => v,
        ToSqlOutput::Owned(ref v) => ValueRef::from(v),
    };
    // TODO: bind more
    let rc = match value {
        //
        // Some code...
        //
        _ => unreachable!("not supported: {}", value.data_type()),
    };
    result_from_duckdb_prepare(rc, ptr)
}

And I find we do not deal with the Decimal, and then panic like:

internal error: entered unreachable code: not supported: Decimal

Can I send you a PR to deal with it?