Added a new Dart class called `RunDetails` to represent specific details related to a benchmark run.
The class includes fields for:
- The unique run identifier (`runId`)
- The command used to initiate the benchmark (`command`)
- The time the benchmark was completed (`completionTime`)
- The time the benchmark started (`benchmarkStartTime`)
- The name of the test being run (`testName`)
Serialization and deserialization methods are also provided for JSON compatibility.
