fix: add timeout to gRPC provider Cleanup to prevent scan hang

[MaheshYadlapati]

Fixes #1653

Problem

driftctl scan hangs after completing all resource enumeration in certain
environments (containerised, slow networks, CI). The scan completes
successfully but the process never exits.

Root Cause

Cleanup() in enumeration/remote/terraform/provider.go calls
client.Close() as a bare blocking call with no timeout:

func (p *TerraformProvider) Cleanup() {
    for alias, client := range p.grpcProviders {
        logrus.WithFields(...).Debug("Closing gRPC client")
        client.Close()  // blocks indefinitely
    }
}

The debug output from affected users confirms the scan completes and
reaches "Closing gRPC client alias=eu-north-1" — the hang is on that
call in environments where gRPC shutdown does not return cleanly.

Fix

Wrap client.Close() in a goroutine with a 5-second timeout. If the
close does not complete within the timeout, a warning is logged and
execution continues rather than blocking forever.

No new imports required — time and plugin are already imported.

Testing

Existing test suite unchanged. The fix is isolated to the shutdown path
and does not affect any resource enumeration or drift detection logic.

[CLAassistant]

All committers have signed the CLA.

[snyk-io]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scan Engine	Critical	High	Medium	Low	Total (0)
✅	Code Security	0	0	0	0	0 issues

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[MaheshYadlapati]

Hi team, raised this PR to address #1653. @MaraDascalu01, would really appreciate a review and approval when you get a chance.

[MaheshYadlapati]

@MaraDascalu01 , Please review and approve the PR