fix: correct timestamp calculation in dify instrumentation

[minimAluminiumalism]

Description

Remove duplicate microsecond calculation. The datetime.timestamp() method already includes microseconds in its decimal portion.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Test A

Does This PR Require a Core Repo Change?

• Yes. - Link to PR:
• No.

Checklist:

See contributing.md for styleguide, changelog guidelines, and more.

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

[Cirilla-zmh]

Thank you for this PR!

@hieheihei Could you please help review this?

[hieheihei]

LGTM

[ralf0131]

Please fix the CI failure before we merge this PR.

[Cirilla-zmh]

This PR may not need a change log, let's ignore it. Thanks for your work! @minimAluminiumalism