Some minor improvements to the scala code

[teigen]

The result is slightly faster parsing and much faster serialization

• close files after reading with Using.resource
• stop splitting lines by comma after reaching enough elements
• simplify index-creation by using getOrElseUpdate
• scala3-style indentation over curly brackets
• use += over addOne as most scala-code tends to do
• avoid double lookup in schedulesForRoute, by looping over both the option and its content
• switched from upickle to jsoniter-scala to improve serialization speed
• added application/json content-type