More consolidations on Hiero OTIO exporter

[robin-ynput]

Changelog Description

help resolve #29

• We were loosing some accuracy on OTIO export for source range start_time, this was causing rounding issues with longest frame range.

Additional review information

TBD

Testing notes:

1. Create a clip in Hiero with a long frame range (e.g. start_frame > 900,000 at 24.0 fps)
2. Drag and drop on a 23.976 sequence while preserving clip duration
3. Trim clip to specific frame input output
4. Export sequence to OTIO and ensure source range of the clip match input frame when rescaled back to 24.0 fps