[Feature]: better use more data for auto-sheme which involves 2 bits

### Feature Description

an average bit-width of 2.5 (options are W2A16G128 and W3A16G128), accounting for scale and zero-point bits. Tuning is employed.

### Motivation and Use Case

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### Alternatives Considered

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### Definition of Done

_No response_

### Additional Context

_No response_