Db2 dialect added

[ShubhamKapoor992]

New Code for Db2 dialect added. I have modified the

"sqlglot/expressions.py"

because

The issue was introduced by commit b3b36baf (Jan 23, 2026) titled "fix(parser)!: robust representation of negative numbers (#6833)". 

The new code calls expr.to_py() on line 2615, which tries to convert the literal to a Python number. When ibis-framework's Oracle compiler calls Literal.number("binary_double_nan"), the to_py() method fails because:

It tries int("binary_double_nan") → ValueError
Then tries Decimal("binary_double_nan") → InvalidOperation
"binary_double_nan" is a special Oracle literal (not a regular number), so it can't be converted to int or Decimal.

Solution:

The to_py() method needs to handle special numeric literals that aren't valid Python numbers. The fix catches the Decimal conversion exception and returns the string as-is for special literals like binary_double_nan.

Please Review.