Add started_at

[Marenz]

• Use correct form of logging
• Reset release notes
• Add Dispatch.started_at(now)

[Copilot]

Pull Request Overview

Adds a new deterministic-start check for Dispatch, standardizes logging in fake service tests, and resets release notes to templates.

• Introduce Dispatch.started_at(now: datetime) and update started to delegate to it
• Replace direct logging.debug calls with module-level _logger in fake service tests
• Clear out RELEASE_NOTES.md content and insert placeholder comments

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/frequenz/client/dispatch/types.py	Added started_at method and routed started through it
src/frequenz/client/dispatch/test/_service.py	Defined _logger and updated debug calls in streaming tests
RELEASE_NOTES.md	Reset notes and added placeholder comments for summary/upgrade

Comments suppressed due to low confidence (2)

src/frequenz/client/dispatch/types.py:432

• No unit tests cover the new started_at method. Add tests for scenarios before start, during active period, after end, inactive dispatches, and recurring dispatches to ensure correct behavior.

    def started_at(self, now: datetime) -> bool:

RELEASE_NOTES.md:5

• Release notes are left as placeholders. Please provide a concise summary of the changes and upgrade instructions before merging.

<!-- Here goes a general summary of what this release is about -->