Refactor PR - Remove global variable and get_writer() function

[payalcha]

This PR is just to refactor the code in different utils.py which is using SummaryWriter.

1. Removal of Global variable usage.
2. removal of get_writer function. As it is not used anywhere else except write_metric.
3. Directly initializing the writer variable.

[MasterSkepticista]

For all taskrunner example updates in this PR: this function will no longer be required, since a TensorBoard callback will internally maintain a writer object and necessary functions to write scalars.

In summary, this (including imports) can be removed too.

[MasterSkepticista]

All this can be removed as well.

P.S: Creating a writer inside write_metric will create a new file handle on each call, which is slow and wasteful. What I meant was to create a function that creates a writer, passes it to a function and returns it. Example:

def get_metric_writer(log_dir: str = "./logs"):
  writer = SummaryWriter(log_dir)

  def _write_scalar(node_name, task_name, metric_name, metric, round_number):
    writer.add_scalar(f"{node_name}/{task_name}/{metric_name}", metric, round_number)

  return _write_scalar

Anyways, this also needs to be removed because it will be taken care of, in TensorBoard callback