refactor(storage): new storage file structure

- new directory structure containing manifest.json and one json file per provider, by default.
- the manifest.json file can specify a filepath for each vpn provider
- each vpn provider json data file can contain the `"preferred": true` field to enforce it is used even if outdated, unless there is a version mismatch
- `STORAGE_SERVERS_DIRECTORY_PATH` replaces `STORAGE_FILEPATH` (which is now a migration source only). It sets the directory where server manifest and per-provider JSON files are stored (default: `/gluetun/servers/`).
- First-run migration: On startup, gluetun checks for the old /gluetun/servers.json file; if found and no new manifest exists, it automatically migrates all data to /gluetun/servers/ directory structure
- Silent fallback: If legacy file isn't found, uses the new directory path normally
- Legacy cleanup: After successful migration, attempts to remove the old fat JSON file (logs warning only if removal fails, e.g., read-only bind mounts)

gluetun-servers/pkg/updaters/providers/purevpn/compare_test.go

@@ -0,0 +1,51 @@
+package purevpn
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_comparePlaceNames(t *testing.T) {
+	t.Parallel() // Allow the top-level test to run in parallel
+
+	testCases := map[string]struct {
+		a    string
+		b    string
+		want bool
+	}{
+		"exact_match": {
+			a:    "Paris",
+			b:    "Paris",
+			want: true,
+		},
+		"difference_in_casing_and_whitespace": {
+			a:    "  Montreal",
+			b:    "montreal  ",
+			want: true,
+		},
+		"accent_normalization": {
+			a:    "Montréal",
+			b:    "Montreal",
+			want: true,
+		},
+		"single_character_typo": {
+			a:    "Lyon",
+			b:    "Lyonn",
+			want: true,
+		},
+		"too_many_differences": {
+			a:    "London",
+			b:    "Londres",
+			want: false,
+		},
+	}
+
+	for name, testCase := range testCases {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+			result := comparePlaceNames(testCase.a, testCase.b)
+			assert.Equal(t, testCase.want, result)
+		})
+	}
+}