pw_console: Fix progress bar division by zero

In some cases it is possible to render a pw_console progress bar while
the elapsed time is still zero. This causes a divide by zero error:

  File
  ".../python-venv/lib/site-packages/prompt_toolkit/shortcuts/progress_bar/formatters.py",
  line 325, in <listcomp>
    len(f"{c.items_completed / c.time_elapsed.total_seconds():.2f}")
Exception float division by zero

The background on why this is an issue is that pw_console removes the
required context manager of prompt_toolkits progress bar
implementation:
https://github.com/prompt-toolkit/python-prompt-toolkit/blob/master/src/prompt_toolkit/shortcuts/progress_bar/base.py#L6
So new runtime errors are possible depending on how the pw_console
start_progress and update_progress functions are
used. https://cs.opensource.google/pigweed/pigweed/+/main:pw_console/py/pw_console/progress_bar/__init__.py

Change-Id: Ifb81038bc838a919f72c2d8f86509bb35edb5016
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/233033
Docs-Not-Needed: Anthony DiGirolamo <[email protected]>
Pigweed-Auto-Submit: Anthony DiGirolamo <[email protected]>
Lint: Lint 🤖 <[email protected]>
Commit-Queue: Auto-Submit <[email protected]>
Presubmit-Verified: CQ Bot Account <[email protected]>
Reviewed-by: William Abajian <[email protected]>

pw_console/py/pw_console/progress_bar/progress_bar_impl.py

@@ -18,6 +18,7 @@
 
 from __future__ import annotations
 
+from datetime import datetime, timedelta
 import functools
 from typing import (
  Iterable,
@@ -167,5 +168,8 @@ def __call__(
  remove_when_done=remove_when_done,
  total=total,
  )
+ # Ensure the elapsed time for the progress counter isn't ever
+ # zero by making the start time one second in the past.
+ counter.start_time = datetime.now() + timedelta(seconds=-1)
  self.counters.append(counter)
  return counter