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

[wenhuach21]

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