Raise more informative ROBOT error

[bgyori]

I've often been confused by the error shown if Robot conversion fails since it doesn't show the actual output from Robot so the reason for the error is unclear:

CalledProcessError: Command '['java', '-jar', '/Users/ben/.data/robot/1.9.7/robot.jar', 'merge', '-i',
 '/Users/ben/.data/pyobo/raw/bao/bao_complete.owl', 'convert', '-o', 
'/Users/ben/.data/pyobo/raw/bao/bao_complete.obo']' returned non-zero exit status 1.

There are two challenges: subprocess.CalledProcessError doesn't surface the output by default and the output can be very long which if fully displayed would be disruptive. So this PR adds a custom RobotError class which is raised instead of subprocess.CalledProcessError and creates a nicer and easier-to-customize output:

RobotError: Command ['java', '-jar', '/Users/ben/.data/robot/1.9.7/robot.jar', 'merge', '-i', 
'/Users/ben/.data/pyobo/raw/bao/bao_complete.owl', 'convert', '-o', 
'/Users/ben/.data/pyobo/raw/bao/bao_complete.obo'] returned non-zero exit status 1.
Output: OBO STRUCTURE ERROR Ontology does not conform to OBO structure rules:
multiple name tags not allowed. in frame:Frame(null ontology( http://www.bioassayontology.org/
bao/bao_complete.owl)data-version( http://www.bioassayontology.org/bao/bao_complete.owl)
property_value( dc:date March20, 2025 xsd:string)property_value( dc:license 
https://creativecommons.org/licenses/by-sa/4.0/)remark( Contact: Stephan Schurer stephan 
dot schurer at med dot miami dot edu)remark( Created by: Caty Chung, Nicolette Ross...

by default showing up to 500 characters of the actual Robot error.

Fixes #10 though taking a different approach to the one suggested there.

[cthoyt]

thanks!

[joeflack4]

@bgyori Much appreciated!