Add support for experiments (previously named timecourses)

[dilpath]

• [ ] functionality
  • [X] read/write
  • [X] OOP
  • methods for tools
    • [ ] to_events
    • [ ] to_sequence_of_petab
    • [ ] to_single_petab_and_sequence_of_metadata
    • [ ] optimize_metadata_to_reduce_redundant_simulations
    • [ ] optimize_metadata_to_reduce_events_or_unique_petabs_in_sequence_of_petabs
• [ ] linter validation checks
• [ ] test all functionality
• [ ] docs