feat(sensors_plus): Add support for platform timestamp in event

[Ortes]

Description

Add timestamp to events from plateform instead of using DateTime.now() at event arrival that can suffer from jitter.
This can be useful to make fft or signal analysis.

I would start this PR as a discussion about the usefulness of this feature or how to implement it

I will provide the iOS implementation in the next few days

Related Issues

• Fix Consider adding timestamps to sensor events flutter/flutter#26078 event if it is not the same repo the problem is the same

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I titled the PR using Conventional Commits.
• I did not modify the CHANGELOG.md nor the plugin version in pubspec.yaml files.
• All existing and new tests are passing.
• The analyzer (flutter analyze) does not report any problems on my PR.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• [~] Yes, this is a breaking change (please indicate that with a ! in the title as explained in Conventional Commits).
• No, this is not a breaking change.
• The API change but most sensor streams users won't need to change anything (if you don't create events like UserAccelerometerEvent)