Draft: CI: Enable cell sequence range simulation to catch bigint overflow

What does this MR do and why?

CI: Enable cell sequence range simulation to catch bigint overflow

• Extract reusable alter_sequences_range task from cell-specific version
• Configure db:migrate:reset to simulate cell-2 sequence ranges (100B-200B)
• Surface potential integer column overflow issues before production

Draft?

• Add specs for the new rake task

References

• Closes Run the RSpec test suite with large sequence ra... (#569682 - closed)

How to set up and validate locally

1. Reset database - bundle exec rake db:drop db:setup
2. Check current min/max values. gdk psql

gitlabhq_development=# SELECT DISTINCT min_value, max_value FROM pg_sequences ORDER BY min_value, max_value;
 min_value |      max_value
-----------+---------------------
         1 | 9223372036854775807
      1000 | 9223372036854775807
(2 rows)

3. Apply sequence ranges to simulate a cell (cell-2)

$ bundle exec gitlab:db:alter_sequences_range[100_000_000_001,200_000_000_000]

4. Re-check current min/max values. gdk psql

gitlabhq_development=# SELECT DISTINCT min_value, max_value FROM pg_sequences ORDER BY min_value, max_value;
  min_value   |  max_value
--------------+--------------
 100000000001 | 200000000000
(1 row)

5. Seed database via bundle exec rake db:seed_fu
6. No errors ✅

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