Fix size validation for volumes from snapshots with decimal units

[deepakkinni]

What this PR does / why we need it:

Fixes a bug where creating a LinkedClone PVC from a VolumeSnapshot fails when using decimal storage units (G) instead of binary units (Gi).

The issue occurred because the size validation was comparing raw byte values instead of the rounded MB values that CNS actually uses for provisioning. When a user creates a PVC with 25G (25,000,000,000 bytes), the CSI driver rounds this to 23,842 MB for CNS provisioning. However, the old validation compared the raw byte value (25,000,000,000) against the snapshot size in bytes (23,842 MB * 1,048,576), causing a mismatch and rejecting the restore.

This fix changes the validation to compare the rounded MB values instead, ensuring that LinkedClone PVCs created with the same decimal size specification as the source PVC will succeed.

Changes:

• Modified createBlockVolume in pkg/csi/service/wcp/controller.go to compare volSizeMB with snapshotSizeInMB (both after rounding) instead of comparing raw byte values
• The validation now enforces strict equality on rounded MB values, which is what CNS actually provisions

Testing done:

Pre-checkins:
PASS WCP https://jenkins-vcf-csifvt.devops.broadcom.net/job/wcp-instapp-e2e-pre-checkin/700/
PASS VKS https://jenkins-vcf-csifvt.devops.broadcom.net/job/vks-instapp-e2e-pre-checkin/645/

Added comprehensive unit tests in pkg/csi/service/wcp/controller_test.go:

• TestCreateVolumeFromSnapshotWithDecimalUnits with 4 sub-tests:
  • SameDecimalSize: Create 25G PVC → snapshot → 25G LinkedClone ✅ PASS
  • LargerSize: Create 25G PVC → snapshot → 27G LinkedClone ❌ FAIL (as expected)
  • SmallerSize: Create snapshot → smaller LinkedClone ❌ FAIL (as expected)
  • ExactSnapshotSize: Create snapshot → exact size LinkedClone ✅ PASS

All existing snapshot tests continue to pass:

• TestWCPCreateDeleteSnapshot ✅ PASS
• TestCreateVolumeFromSnapshot ✅ PASS

Special notes for your reviewer:

N/A

Release note:

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[deepakkinni]

Triggering CSI-WCP Pre-checkin Pipeline for this PR... Job takes approximately an hour to complete
Jenkins Build #700

[deepakkinni]

Triggering CSI-TKG Pre-checkin Pipeline for this PR... Job takes approximately an hour to complete
Jenkins Build #645

[deepakkinni]

SUCCESS --- Jenkins Build #645

[deepakkinni]

Triggering CSI-WCP Pre-checkin Pipeline for this PR... Job takes approximately an hour to complete
Jenkins Build #716

[deepakkinni]

SUCCESS --- Jenkins Build #717

[deepakkinni]

Not needed. Size difference is checked in external provisioner