.veg (Magix Vegas) support

## Feature Request

Is this a New Feature, or a Proposed Change to existing Behavior?
new feature

## Description

Describe the new feature, or describe the modification to existing behavior, and provide context as necessary to help with understanding how the feature relates to a workflow or functionality.
I would love to be able to convert from and to sony vegas. I like kdenlive but its import and export function does not work at all. and otioconvert dont know how to make it work, says otioconvert -i j.kdenlive -o a.xml
Traceback (most recent call last):
File "/home/d-ri/.local/bin/otioconvert", line 8, in
sys.exit(main())
File "/home/---/.local/lib/python3.10/site-packages/opentimelineio/console/otioconvert.py", line 243, in main
result_tl = otio.adapters.read_from_file(
File "/home/-i/.local/lib/python3.10/site-packages/opentimelineio/adapters/__init__.py", line 137, in read_from_file
return adapter.read_from_file(
File "/home/-/.local/lib/python3.10/site-packages/opentimelineio/adapters/adapter.py", line 119, in read_from_file
result = self._execute_function(
File "/home/d-i/.local/lib/python3.10/site-packages/opentimelineio/plugins/python_plugin.py", line 153, in _execute_function
return (getattr(self.module(), func_name)(**kwargs))
File "/home/d-/.local/lib/python3.10/site-packages/opentimelineio_contrib/adapters/kdenlive.py", line 237, in read_from_string
raise RuntimeError("Can't find main tractor")
RuntimeError: Can't find main tractor

## Context

Start by reproducing the reported otioconvert command and reviewing the kdenlive adapter traceback, especially the failure to find the main tractor. Determine the requirements for reading and writing Sony Vegas .veg timelines, then add coverage demonstrating successful conversion in both directions.

Written by the indexing model from the issue text.