Weighted Median Partition Threshold

You are given two sorted arrays `groupA` and `groupB` of integers (not necessarily the same length). Each element has an associated weight of 1. Find the **median** of the combined dataset formed by merging both arrays.

If the combined count of elements is odd, return the single middle value. If even, return the average of the two middle values.

You must solve this in **O(log(min(m, n)))** time, where `m` and `n` are the lengths of `groupA` and `groupB`.

**Example 1:**
```
Input: groupA = [1, 4, 8], groupB = [2, 6, 9, 11]
Output: 6.0
Explanation: Merged sorted array: [1, 2, 4, 6, 8, 9, 11]
Median (7 elements): index 3 → 6.
```

**Example 2:**
```
Input: groupA = [3, 10], groupB = [5, 7]
Output: 6.0
Explanation: Merged sorted array: [3, 5, 7, 10]
Median (even): (5 + 7) / 2 = 6.0.
```