size based load balancing: add test

[cezarmoise]

Warning

DRAFT

Test to ensure that the cluster is balanced correctly in difficult conditions:

• heterogeneous nodes with different disk sizes.
• multiple tables with different partition sizes.

This test will:

1. Expand the cluster by adding new nodes.
2. Run the original test_custom_time to populate the cluster with data.
3. Wait for tablet migration to finish.
4. Check the disk usage of each node to ensure they are balanced.

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Cluster setup: 1 DC, 3 racks, 3 nodes per rack (1x i4i.large, 1x i4i.xlarge, 1x i4i.2xlarge)
The test creates 3 tables:

• table 1
  • 200000 x 1MB partitions
  • 10000 x 10MB partitions
  • 200 x 1GB partitions
  • 10 x 10GB partitions
• table 2
  • 100000 x 1MB partitions
  • 2000 x 100MB partitions
  • 100 x 1GB partitions
  • 2 x 100GB partitions
• table 3
  • 20000 x 10MB partitions
  • 1000 x 100MB partitions
  • 20 x 10GB partitions
  • 1 x 100GB partitions

Testing

• Scylla version: 2025.3.0~dev-20250527.efce03ef43b1
  

PR pre-checks (self review)

• I added the relevant backport labels
• I didn't leave commented-out/debugging code

Reminders

• Add New configuration option and document them (in sdcm/sct_config.py)
• Add unit tests to cover my changes (under unit-test/ folder)
• Update the Readme/doc folder relevant to this change (if needed)

[scylladbbot]

@cezarmoise new branch manager-3.6 was added, please add backport label if needed

[scylladbbot]

@cezarmoise new branch branch-2025.3 was added, please add backport label if needed