overview: fix "internal error: no overview data found" on 32 bit architectures - fixes #9723

The precision field in the backend overview YAML files can hold
fs.ModTimeNotSupported (100 years in nanoseconds) which overflows int
on 32 bit platforms, making the YAML for those backends fail to parse
and causing rclone to log 18 internal errors on every invocation.

Use int64 for the precision field and add a test that parses every
embedded backend YAML file so this is caught on 32 bit test runs.

backend/overview/overview.go

@@ -26,7 +26,7 @@ type BackendConfig struct {
 	Remote           string   `yaml:"remote"`
 	Features         []string `yaml:"features"`
 	Hashes           []string `yaml:"hashes"`
-	Precision        int      `yaml:"precision"`
+	Precision        int64    `yaml:"precision"`
 }
 
 // GetBackendConfig from docs/data/backends

backend/overview/overview_test.go

@@ -1,8 +1,10 @@
 package overview
 
 import (
+	"strings"
 	"testing"
 
+	"github.com/rclone/rclone/docs/data/backends"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -53,3 +55,17 @@ func TestGetBackendConfig(t *testing.T) {
 	assert.Equal(t, expectedMemoryConfig, conf, "parsed memory.yaml should match")
 
 }
+
+// Check every embedded backend YAML file parses on all architectures
+func TestGetBackendConfigAll(t *testing.T) {
+	entries, err := backends.BackendFS.ReadDir(".")
+	require.NoError(t, err)
+	require.NotEmpty(t, entries)
+
+	for _, entry := range entries {
+		name := strings.TrimSuffix(entry.Name(), ".yaml")
+		conf, err := GetBackendConfig(name)
+		assert.NoError(t, err, "failed to load %s", entry.Name())
+		assert.NotNil(t, conf)
+	}
+}