fix: driver and toolkit ready state file cleanup

[shivakunv]

Description

Fix stale readiness file handling for driver and toolkit operands during restart/upgrade flows.

During upgrade, the old driver-ready and toolkit-ready files can remain on the host because unlike .driver-ctr-ready, they were not being cleaned up during pod shutdown.
mig-manager only waits for those files to exist, not for new validation of the new driver/toolkit state.
So after driver reinstall: mig-manager can start using old ready signals before the new driver/toolkit libraries are actually available.
files are only deleted when the corresponding validator runs again:

toolkit-ready :

func (t *Toolkit) validate() error {
	// delete status file is already present
	err := deleteStatusFile(outputDirFlag + "/" + toolkitStatusFile)
	if err != nil {
		return err
	}

driver-ready:

func (d *Driver) validate() error {
	// delete driver status file if already present
	err := deleteStatusFile(outputDirFlag + "/" + driverStatusFile)
	if err != nil {
		return err
	}

The patch fixes that by cleaning up driver-ready and toolkit-ready file.

Checklist

• No secrets, sensitive information, or unrelated changes
• Lint checks passing (make lint)
• Generated assets in-sync (make validate-generated-assets)
• Go mod artifacts in-sync (make validate-modules)
• Manual validation on hardware with MIG-capable GPUs

Testing

Reproduction in a test environment was not possible because the issue appears to be timing-dependent and hard to reproduce reliably.
Validation for this change was done by code-path analysis.
I will perform manual validation on hardware with MIG-capable GPUs

[coveralls]

coverage: 27.711%. remained the same
when pulling 21d3d41 on cleanupdriverreadyfile
into d5750f2 on main.

[shivakunv]

PTAL @rahulait @rajathagasthya