✨ feat: add background execution for emails and Slack notifications

[abdullai-t]

Summary / Highlights

This pull request adds background execution for email and Slack notifications for better performance, and enhanced logging for email errors.

Details (Give details about what this PR accomplishes, include any screenshots etc)

https://github.com/user-attachments/assets/59cb844c-9513-4bab-87d1-d8dc369432ef

Testing Steps (Provide details on how your changes can be tested)

Requirements (place an x in each [ ])

• [x] I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• [x] I've tested my changes manually.
• [ ] I've added unit tests to my PR.

Transparency (Project board)

• [ ] I've given my PR a meaningful title.
• [ ] I linked this PR to the relevant issue.
• [ ] I moved the linked issue from the "Sprint backlog" to "In progress" when I started this.
• [ ] I moved the linked issue to "QA Verification" now that it is ready to merge.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.

Project coverage is 55.74%. Comparing base (366cba8) to head (0fad127). Report is 1 commits behind head on main.

Files	Patch %	Lines
src/_main_/utils/emailer/send_email.py	60.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1155 +/- ## ======================================= Coverage 55.74% 55.74% ======================================= Files 461 461 Lines 33886 33891 +5 ======================================= + Hits 18890 18893 +3 - Misses 14996 14998 +2 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.