[BUG] Azure Migrate Explore fails to generate performance-based assessment outputs due to parsing error on confidenceRatingInPercentage

### Release version

AzureMigrateExplore-v4.0.25280.1

### Describe the bug

When running a csv import-based express workflow assessment using Azure Migrate Explore (AME), the tool fails to generate performance-based outputs (Perf worksheets and Financial_Summary) due to a parsing error. This results in incomplete XLSX reports and missing visuals in the Power BI dashboard.

### Expected behavior

AME should gracefully handle null values in confidenceRatingInPercentage or provide fallback logic to avoid breaking the assessment pipeline.

### Actual behavior

- Perf-based sizing is skipped entirely.
- Financial modelling is not generated.
- Power BI visuals relying on these datasets are blank

### Reproduction Steps

1. Upload a CSV to Azure Migrate containing mandatory fields and additional performance data (CPU, memory utilization).
2. Use AME to run an import-based express workflow assessment targeting IaaS, PaaS, and AVS.
3. Select “Minimize time with Azure VM” as the migration strategy.
4. Observe that the generated AzureMigrate_Assessment_Core_Report.xlsx lacks data in all _Perf worksheets and the Financial_Summary tab.
5. Review AME logs and find the following error and warnings:

```
ERROR Azure VM assessment parsing error Error converting value {null} to type 'System.Double'. Path 'value[0].properties.confidenceRatingInPercentage', line 1, position 2566.
WARN Not creating excel model for All_VM_IaaS_Server_Rehost_Perf as Azure VM Perf dataset is empty
WARN Encountered an issue while processing All_VM_IaaS_Server_Rehost_Perf excel model
WARN Not generating excel model for VM_IaaS_Server_Rehost_Perf as Azure VM Perf dataset is empty
WARN Encountered issue while generating excel model for VM_IaaS_Server_Rehost_Perf
```

### Environment

- AME version: AzureMigrateExplore-v4.0.25280.1
- Assessment type: Import-based express workflow
- Migration strategy: Minimize time with Azure VM
- Input: CSV with performance data included (CPU and Memory Utilization)