fix: add compatibility for reading non-standard decimal256 format

[dantengsky]

I hereby agree to the terms of the CLA available at: https://docs.databend.com/dev/policies/cla/

Summary

add compatibility for reading non-standard decimal256 format.

to be detailed

Tests

• Unit Test
• Logic Test
• Benchmark Test
• No Test - manually test

Type of change

• Bug Fix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Breaking Change (fix or feature that could cause existing functionality not to work as expected)
• Documentation Update
• Refactoring
• Performance Improvement
• Other (please describe):

---

This change is