Given two strings `s` and `t` of lengths `m` and `n` respectively, return the **minimum window substring** of `s` such that every character in `t` (including duplicates) is included in the window. If there is no such substring, return the empty string `""`.
**Example 1:**
```
Input: s = "ADOBECODEBANC", t = "ABC"
Output: "BANC"
```
**Example 2:**
```
Input: s = "a", t = "a"
Output: "a"
```
**Example 3:**
```
Input: s = "a", t = "aa"
Output: ""
```