Set the time zone in main and run Entry in its own test process (closes #192)

cli.Entry() set time.Local to UTC and ended with memguard.Purge(), and
TestEntryWipesBuffersAndReturnsExitCode ran it in the same process as
the other tests. A timer left by an earlier test could read time.Local
as it changed, which the race detector reported on some runs, and the
purge could destroy a buffer still in use, the likeliest cause of a
crash seen on another run.

main() in cmd/secret now sets time.Local before it calls cli.Entry();
the test that runs the built binary with TZ=America/New_York still
covers it. The Entry test runs cli.Entry() in a copy of the test binary
started with SECRET_TEST_RUN_ENTRY set, which init picks up so that
TestMain does not run there.

Model: opus-5-5

internal/cli/root.go

@@ -2,7 +2,6 @@ package cli
 
 import (
 	"os"
-	"time"
 
 	"github.com/awnumar/memguard"
 	"github.com/spf13/cobra"
@@ -15,10 +14,6 @@ import (
 // every memguard buffer before it returns, so the caller must do nothing
 // but exit with the code.
 func Entry() int {
-	// Every time secret prints or writes is in UTC, whatever TZ or the
-	// system's time zone is set to.
-	time.Local = time.UTC //nolint:gosmopolitan // this makes local time UTC
-
 	raiseLockedMemoryLimit()
 
 	// On SIGINT or SIGTERM memguard runs this function, wipes every buffer