Y24-120 Part-2 Bug taken link error when creating sequencing batches

[yoldas]

Closes #

Changes proposed in this pull request

• Database migration to add a unique-together on asset_links ancestor_id and descendant id
• Override AssetLink's create_edge method to handle race conditions

Instructions for Reviewers

[All PRs] - Confirm PR template filled
[Feature Branches] - Review code
[Production Merges to main]
    - Check story numbers included
    - Check for debug code
    - Check version

[codecov]

Codecov Report

Attention: Patch coverage is 65.57377% with 21 lines in your changes missing coverage. Please review.

Project coverage is 87.63%. Comparing base (1bd6131) to head (a9ff092).
Report is 85 commits behind head on develop.

Files with missing lines	Patch %	Lines
...ib/tasks/support/remove_duplicate_asset_links.rake	16.66%	15 Missing ⚠️
app/models/asset_link.rb	78.94%	4 Missing ⚠️
lib/tasks/insdc/import_countries.rake	50.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #4340      +/-   ##
===========================================
- Coverage    87.69%   87.63%   -0.06%     
===========================================
  Files         1395     1397       +2     
  Lines        30038    30097      +59     
===========================================
+ Hits         26343    26377      +34     
- Misses        3695     3720      +25     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[stevieing]

Just one minor issue. Pretty good. I don't entirely understand it but it is well structured and commented.