Implement a two-sample independent t-test (Welch's t-test) to determine if two samples have significantly different means. The test should compute the t-statistic, p-value using the Welch-Satterthwaite degrees of freedom, make a decision to reject or fail to reject the null hypothesis, and calculate Cohen's d effect size. Welch's t-test does not assume equal variances between groups. Given two samples and a significance level alpha, return a dictionary with the test results.