convert dtype of column cudf

# convert just columns "a" and "b" of dataframe(df)
df["a","b"] = cudf.to_numeric(df["a","b"])

# convert ALL columns of DataFrame
df = cudf.to_numeric(df) # convert all columns of DataFrame, 

#dont try `cudf.apply` as it is not supported in cudf API

Here is what the above code is Doing:
1. Convert the column “a” to numeric
2. Convert the column “b” to numeric
3. Convert all columns of DataFrame to numeric

Note:
1. The first two steps are done in parallel.
2. The last step is done in parallel.
3. The first two steps are done in parallel.
4. The last step is done in parallel.