fix column type conversion in SQLite3 driver

[Jumpaku]

I found a bug in the SQLite3 driver related to column type conversion. The issue occurred when a column was not nullable, resulting in incorrect type conversion. Specifically, columns with types such as FLOAT(2, 1) or TYNYINT(1) were wrongly converted to string instead of float32 and int8 (although these types were correctly converted into null.Float32 and null.Int8 when the columns are nullable).

In this pull request, I have addressed this issue by fixing the column type conversion logic for non-nullable columns. Now, even if a column is not nullable, the types FLOAT(2, 1) and TYNYINT(1) are correctly converted to float32 and int8, respectively. Additionally, I have updated the relevant test cases to thoroughly verify that these type conversions work as intended.