fix(oracle): cast string to int for the precision and scale of decimal

[goldmedal]

Description of changes

The type mapping for Oracle number type can't handle the number type with precision and scale.
For example, given a table like

CREATE TABLE "number_table" ("number_8_2" NUMBER(8, 2))

In the Ibis side, we will get Number('8', '2'), we should cast them to int from string.

Issues closed

No corresponding issue currently.

[goldmedal]

E       AssertionError: assert 'ibis_temp_memtable_qkkxzqsisjebxftctnvv4y74yi' not in ['astronauts', 'awards_players', 'batting', 'diamonds', 'functional_alltypes', 'ibis_pandas_memtable_3g6g3sg5lbdvdi36mmyc4hqtde', ...]
E        +  where ['astronauts', 'awards_players', 'batting', 'diamonds', 'functional_alltypes', 'ibis_pandas_memtable_3g6g3sg5lbdvdi36mmyc4hqtde', ...] = list_tables()
E        +    where list_tables = <ibis.backends.exasol.Backend object at 0x7f8801bb2370>.list_tables

I don't understand the CI failure. I just followed test_blob_raw to add the test 🤔.
Could anyone tell me how to fix it? Thanks.

[cpcloud]

LGTM, thanks!