Boot Time Profiler

Turn a boot log with millisecond timestamps into a profile that shows how long each stage took and which stage dominates.

Constraints

• Lines look like '[00123] stage name'.
• A stage's duration is the gap to the next timestamp.
• The last stage has no duration and is reported as 0.
• Return stages sorted by duration, longest first.
• Non-conforming lines are ignored.
• Timestamps that go backwards must raise ValueError.