test(volume): Add unit tests for volume/volumes.go

[adity1raut]

Prerequisite checklist

• Read the contribution guidelines regarding submitting new changes to the project;
• Tested your changes locally.

Description of changes

Summary

• Adds table-driven unit tests for VolumeConfig in unikraft/app/volume/volumes.go
• Achieves 100% coverage across the entire unikraft/app/volume package

Cases tested

• All accessor methods: Driver, Source, Destination, Mode, ReadOnly
• Zero value accessors return correct defaults
• MarshalYAML with all fields populated
• MarshalYAML with only source, destination, or driver set
• MarshalYAML with fully empty config returns nil
• MarshalYAML with readonly=true/false

Related Issue

Closes #2700

Test plan

• Run go test ./unikraft/app/volume/... -cover — 100% coverage

[craciunoiuc]

static checks failing