Ensure timestamp conversion errors are surfaced

[matthias-wende-frequenz]

Added a try...except...raise block around the calls to dt_to_pb_timestamp_utc for start_time and end_time.

Previously, an error during this conversion might not have been handled explicitly at this point. This change guarantees that if the conversion fails, the exception is propagated immediately, improving robustness and aiding debugging by making the failure point clear.

[Copilot]

Pull Request Overview

This PR ensures that errors during timestamp conversion in the electricity trading client are surfaced immediately by adding a try...except...raise block. Key changes include:

• Introducing a try-except block around dt_to_pb_timestamp_utc calls for start_time and end_time.
• Updating the client code to use the converted timestamp variables.
• Reflecting the change in RELEASE_NOTES.md for clarity on how timestamp conversion errors are handled.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/frequenz/client/electricity_trading/_client.py	Wraps timestamp conversion with try...except...raise to propagate errors immediately.
RELEASE_NOTES.md	Updates release notes to include the new behavior on timestamp conversion errors.

[micaebe]

lgtm
But CI is failing bcs. mypy wants to have a tuple of exception classes instead of the | optional notation (so TypeError | ValueError -> (TypeError, ValueError))

[matthias-wende-frequenz]

But CI is failing bcs. mypy wants to have a tuple of exception classes instead of the | optional notation (so TypeError | ValueError -> (TypeError, ValueError))

pylint was also complaining. I removed the whole block and made catching the error less explicit. Calling the dt_to_pb_timestamp_utc function explicitly is enough to propagate the raised error up the call stack.

Now all nox tests are passing 🥳.