need to support float format in cohort results

[KimballCai]

please check the branch support_float_cohort_result

1. update the unit test in the CohortAnalysisTest.java
2. check the CohortRet.java incase there is any potential error left

[tinyAdapter]

I think the current implementation is problematic, as it breaks the original behavior and invalidates some tests.

I suggest adding a new entry in the cohort query file (e.g., resultType) with default value INT to make it backward-compatible, while allow users to specify the system to return float values.

[tinyAdapter]

Resolved in #155