Provide Error Message and Defaults for Missing Fields in link.csv

[asu-trans-ai-lab]

Issue Description:
Currently, when the length, free_speed, or capacity field in the link.csv file is missing, DTALite stops processing. This abrupt termination could be avoided by providing more user-friendly feedback and robust error handling.

Proposed Solution:
If the length, free_speed, or capacity field is missing in link.csv, the program should provide an error message notifying the user of the missing fields. After providing this feedback, the program should use the following default values to continue processing:

length: 999.0 (meters)
free_speed: 60.0 (kmph)
capacity: 1800
Steps to Reproduce:

Remove or clear the length, free_speed, or capacity field in link.csv.
Run DTALite.
Expected Outcome:
The program provides an error message and uses default values to continue processing.

Actual Outcome:
The program stops processing without sufficient error messaging or attempt to use default values.

Additional Information:
Enhancing this aspect of the program would significantly improve its user-friendliness and resilience, ensuring it can still function with incomplete data and providing clear feedback to users when their data is missing necessary fields.