Enable copyloopvar linter and remove redundant variable
shadowing in Kubernetes plugin metadata handling. This pattern is
no longer needed in Go 1.22+ where loop variables are automatically
captured correctly in closures.
Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>
Enable the usetesting linter in golangci.yml configuration to
enforce proper testing practices. Replace manual temporary
directory and file creation with t.TempDir() in test files.
This improves test reliability by ensuring proper cleanup and
follows Go testing best practices.
Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>
