The Frost-Ledges of Skarnholt Glacier

A seam of ice ledges runs across the face of Skarnholt Glacier. The Lodge of Highland Surveyors pays a bounty for every ledge a climber plants a flag on during a single traverse.

The ledges are given west to east in heights, a list of integers. Each integer is one ledge's height in fathoms. Heights may be negative, and the list may be empty.

A traverse is built as follows:

• The climber chooses any subset of the ledges and visits them in their listed order. Any number of ledges may be skipped.
• Each chosen ledge must be strictly higher than the chosen ledge before it.

Write longestAscent(heights). It returns an integer: the largest number of ledges that a single valid traverse can include. An empty list returns 0.