Problem

In Aptive Environmental scheduling, a common algorithm merges overlapping technician service windows. Write a function that takes a list of time intervals and returns a new list with all overlapping intervals merged.

Formal Specification

Implement a function merge_service_windows(windows) where:

• Input: windows, a list of intervals, where each interval is a list [start, end] of integers.
• Output: a list of merged, non-overlapping intervals sorted by start time.

Two intervals overlap if the next interval's start is less than or equal to the current merged interval's end.

Examples

Example 1

• Input: windows = [[1,3],[2,6],[8,10],[15,18]]
• Output: [[1,6],[8,10],[15,18]]
• Explanation: [1,3] and [2,6] overlap, so they merge into [1,6].

Example 2

• Input: windows = [[1,4],[4,5]]
• Output: [[1,5]]
• Explanation: Touching endpoints count as overlapping, so these intervals merge.

Constraints

• 0 <= len(windows) <= 10^4
• windows[i].length == 2
• -10^9 <= start <= end <= 10^9
• The input list may be unsorted.

Testing Task

After implementing the algorithm, write a comprehensive unit test suite. Your tests should verify correctness for normal cases, edge cases, and failure-prone boundaries such as empty input, single intervals, nested intervals, duplicate intervals, and endpoint-touching merges.