Set skew to 1 by default and create a test

[KEINOS]

In our usual case, most of the time the code validation works well.

But, due to the default skew value being as 0, code validation often fails if the period are short.

Here's an example to reproduce. This test will pass if the skew is set to 1.

func TestKey_skew_as_one(t *testing.T) {
	// Backup and defer restore
	oldTimeNow := timeNow
	defer func() {
		timeNow = oldTimeNow
	}()

	key, err := GenerateKey("dummy issuer", "dummy account")
	require.NoError(t, err, "failed to generate TOTP key during test setup")

	key.Options.Period = 3 // 3 seconds
	//key.Options.Skew = 1   // ± 1 period of tolerance

	getCode := func(t *testing.T, key *Key) string {
		t.Helper()

		// Monkey patch timeNow
		timeNow = func() time.Time {
			return time.Now()
		}

		passCode, err := key.PassCode()
		require.NoError(t, err, "failed to generate passcode")

		return passCode
	}

	validateCode := func(t *testing.T, key *Key, passCode string) bool {
		t.Helper()

		// Monkey patch timeNow
		timeNow = func() time.Time {
			return time.Now().Add(time.Second * 200)
		}

		// sleep for 2 sec. This delay causes error/invalid 60% of the
		// time.
		time.Sleep(time.Second * 2)

		return key.Validate(passCode)
	}

	numValid := 0
	numIterations := 10

	for i := 0; i < numIterations; i++ {
		passCode := getCode(t, key)
		ok := validateCode(t, key, passCode)

		if ok {
			numValid++
		}
	}

	expect := numIterations
	actual := numValid

	require.Equal(t, expect, actual,
		"not all generated passcodes are valid")
}

$ go test -timeout 30s -run ^TestKey_skew_as_one$ github.com/KEINOS/go-totp/totp

--- FAIL: TestKey_skew_as_one (20.01s)
    /Users/admin/Library/Mobile Documents/com~apple~CloudDocs/Data_Git/GitHub/PublicRepos/go-totp/totp/issue_44_test.go:64: 
        	Error Trace:	/Users/admin/Library/Mobile Documents/com~apple~CloudDocs/Data_Git/GitHub/PublicRepos/go-totp/totp/issue_44_test.go:64
        	Error:      	Not equal: 
        	            	expected: 10
        	            	actual  : 4
        	Test:       	TestKey_skew_as_one
        	Messages:   	not all generated passcodes are valid
FAIL
FAIL	github.com/KEINOS/go-totp/totp	20.250s
FAIL