[UT] Add SQL tests for mem_pool property of resource groups (backport #65859)

[mergify]

Why I'm doing:

The mem_pool property for resource groups was recently introduced.

• [Feature] Add mem_pool property to resource groups #64111
• [Feature] Use mem_pool property to create shared mem_tracker across resource groups #64112

There are currently no end-to-end SQL test cases for this functionality.

What I'm doing:

This pull request adds SQL tests, checking the correctness of the behavior under the following scenarios:

• test_create_resource_group_with_mem_pool (should succeed)
• test_create_two_resource_groups_with_mem_pool (should succeed)
• test_create_two_resource_groups_with_mem_pool_then_try_alter (not allowed)
• test_create_two_resource_groups_with_mem_pool_different_mem_limit (not allowed)

What type of PR is this:

• BugFix
• Feature
• Enhancement
• Refactor
• UT
• Doc
• Tool

Does this PR entail a change in behavior?

• Yes, this PR will result in a change in behavior.
• No, this PR will not result in a change in behavior.

If yes, please specify the type of change:

• Interface/UI changes: syntax, type conversion, expression evaluation, display information
• Parameter changes: default values, similar parameters but with different default values
• Policy changes: use new policy to replace old one, functionality automatically enabled
• Feature removed
• Miscellaneous: upgrade & downgrade compatibility, etc.

Checklist:

• I have added test cases for my bug fix or my new feature
• This pr needs user documentation (for new or modified features or behaviors)
  • I have added documentation for my new feature or new function
• This is a backport pr

Bugfix cherry-pick branch check:

• I have checked the version labels which the pr will be auto-backported to the target branch
  • 4.0
  • 3.5
  • 3.4
  • 3.3

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Note

Add end-to-end SQL tests validating resource group mem_pool creation, sharing, immutability, and mem_limit constraints.

• SQL tests for mem_pool in resource groups:
  • Creation: Verify creating a resource group with mem_pool succeeds (test_create_resource_group_with_mem_pool).
  • Shared pool: Validate two groups can share the same mem_pool with matching mem_limit (test_create_two_resource_groups_with_mem_pool).
  • Constraints:
    • Reject creating a second group in the same mem_pool with a different mem_limit (test_create_two_resource_groups_with_mem_pool_different_mem_limit).
    • Disallow altering mem_pool and mem_limit once set; allow changing max_cpu_cores (test_create_resource_group_with_mem_pool_then_try_alter, test_create_two_resource_groups_with_mem_pool_then_try_alter).
  • Added corresponding R/ expected-result files with regex assertions and error codes.

^{Written by Cursor Bugbot for commit 6f8a6c8. This will update automatically on new commits. Configure here.}

---

This is an automatic backport of pull request #65859 done by [Mergify](https://mergify.com).

[mergify]

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