Fix DECFLOAT conversion for fetch APIs (#1075)

[Earammak]

Fix DECFLOAT bound-column buffer allocation

The issue was caused by allocating the bound-column buffer based on the column display size. In some cases, the display size was insufficient for the DECFLOAT string representation generated by the CLI conversion routines, resulting in fetch failures.

Fix:

• Use MAX_DECFLOAT_LENGTH to allocate sufficient buffer space for DECFLOAT values.
• Ensure adequate space for DECFLOAT value conversion during fetch operations.
• Prevent fetch failures when DECFLOAT values have longer string representations.