Implements a new model for test results, to allow for cleaner recursive outputs in callers

[Varun0157]

• adds a SpecResult model and moves the spec attribute from TestResult to SpecResult, such that we have the following model:

export interface SpecResult {
  spec: string | null;
  results: TestResult[];
  subResults: SpecResult[];
}

Thus, if the caller (curr: vscode extension or cli) wants to flatten out the path invoked on an object, this is possible, or if the caller wants to print an indented output for subsequent layers, this is also possible.