Add timeline axis with multi-unit support to XY charts

- Add configurable timeline bar below XY charts with D3.js
- Support multiple unit types: time, cycles, bytes, calls, data rates
- Include automatic unit formatting (bytes/KB/MB/GB, rates)
- Add timeline props: timelineUnit and timelineUnitType
- Update timeline on chart resize and data changes
- Handle log scaled time

Note: this patch was made with the assistance of claude-sonnet-4

Signed-off-by: Matthew Khouzam <matthew.khouzam@ericsson.com>

Author: MatthewKhouzam