fix(postgres): randomize test_reader username to prevent CI collisions

[sakshipatil-hue]

Description

Resolves #5972. Appended a random UUID suffix to the Postgres test user creation logic to ensure parallel integration tests are completely isolated and do not collide.

Test Plan

Ran the test suite locally to ensure the user creation logic executes without syntax errors.

Checklist

• I have run make style and fixed any issues
• I have added tests for my changes (if applicable)
• All existing tests pass (make fast-test)
• My commits are signed off (git commit -s) per the DCO

[cmgoffena13]

@sakshipatil-hue - you'll need to sign your commits off with DCO

[sakshipatil-hue]

@cmgoffena13 I have amended the commit to include the DCO sign-off and ran the formatting tools to fix the style issues. Could you please approve the workflow run for the latest commit when you get a chance.

[cmgoffena13]

@sakshipatil-hue -- way too many changes here, seems like you triggered formatting with different config.

[sakshipatil-hue]

Hi @cmgoffena13 , I’ve cleaned up the branch to remove the accidental formatting changes, leaving only the Postgres integration test fix with a proper DCO sign-off. Ready for review whenever you're free!

[cmgoffena13]

@sakshipatil-hue -- the ruff format/lint is failing. Make sure you've run make style so its compliant. Look at what files changed too so we don't run into the same issue as before. You can comment on here if you need help. Might be easier to recreate a new branch / PR.

The postgres test is failing. Some of the tests are still granting on the old username since its hardcoded.

Tests that need adjusted:

• test_grants_plan_target_layer_physical_only
• test_grants_plan_target_layer_virtual_only

Look at test_grants_plan_full_refresh_model_via_replace for an example of how some tests already reference the username correctly