Add task times in costs

[jcoupey]

Issue

Fixes #1130

Tasks

• Add new cost factor in VehicleCosts
• Parse new cost factor at vehicle level in json input
• Add task cost in output
• Extend eval struct to include a task cost component
• Update route_eval_for_vehicle to include task costs
• Store necessary forward/backward task costs in SolutionState
• Update node_gains to include task cost delta
• Update addition_cost (simple job insertion version) to include task cost delta
• Update addition_cost (pickup insertion version) to include task cost delta
• Update addition_cost_delta (job insertion version) to include task cost delta
• Update addition_cost_delta (range insertion version) to include task cost delta
• Update in_place_delta_cost to include task cost delta
• Adjust cost evaluation in heuristics
• Benchmark and test
• Update docs/API.md
• Update CHANGELOG.md
• review

EDIT: updated task list after reincorporating the changes from #1267.

[jcoupey]

Now that #1267 is completed, I've merged back the required changes in this feature branch. I'll update the task list accordingly.

[jcoupey]

The current state of this PR looks pretty fine with job-based instances. But we have crashes with shipments since SolutionState::pd_gains does not account for task duration cost variations.