Use ExecOperations in CargoKit Gradle task

[akshaynexus]

Summary

• Replace deprecated project.exec calls in the CargoKit Gradle task with injected ExecOperations.
• Convert the Path executable values to strings for Gradle's exec API.

Why

Gradle 9.x no longer allows this task's project.exec usage during execution. This causes Android release builds that depend on super_native_extensions to fail with:

Could not find method exec() for arguments ... on project ':super_native_extensions'

This patch keeps the behavior the same while using Gradle's task-service exec API.