Allow event_tbl as input of gs_update_ahr

[LittleBeannie]

When updating the boundaries, there are two approaches to consider:

• Approach 1: Input the blinded data. The current gs_update_ahr function will calculate the events for each piecewise interval. These events are then used to calculate the treatment effect (theta) and the statistical information under the alternative hypothesis (info0).
• Approach 2: Input the events for each piecewise interval directly.

Approach 2 is particularly useful when investigating boundaries with event accrual that is faster or slower than planned, without the need for observed data. Additionally, it is beneficial when users already know the summary of event counts.