Update Haste Confidence Interval Formula for Small Sample Sizes

[Pavel-Durov]

The current implementation of confidence intervals in haste uses z-values for all sample sizes. For small sample sizes (n < 30), the t-distribution should be used instead of the z-distribution to provide more accurate confidence intervals.

Using the t-distribution for small samples increases the statistical accuracy of confidence intervals.

Suggested Plan:

• For each benchmark, if the sample size is less than 30, use the t-value corresponding to the confidence level and degrees of freedom (n-1).
• For sample sizes 30 or greater, continue to use the z-value.
• The t-values can be retrieved from a statistical library (e.g., statrs in Rust).