break out rust/bambam/src/app/gtfs_config/run.rs into separate files

[robfitzgerald]

there are a lot of functions (and there should be more, too) in run.rs. cleanup could

• move some operations into their own ops.rs file(s)
• turn parts of the run method into sub-functions for readability
• goal: make it less mystifying what mutable state is being tracked and where it is updated