chore(lint): add new linters and update codebase

- add canonicalheader
- add copyloopvar
- add fatcontext
- add intrange

internal/provider/fastestvpn/updater/api.go

@@ -77,7 +77,7 @@ func fetchAPIServers(ctx context.Context, client *http.Client, protocol string)
 		var server apiServer
 
 		const numberOfTDBlocks = 3
-		for i := 0; i < numberOfTDBlocks; i++ {
+		for i := range numberOfTDBlocks {
 			tdBlock := getNextTDBlock(trBlock)
 			if tdBlock == nil {
 				return nil, fmt.Errorf("%w: expected 3 <td> blocks in <tr> block %q",

internal/provider/fastestvpn/updater/api_test.go

@@ -89,7 +89,6 @@ func Test_fechAPIServers(t *testing.T) {
 	}
 
 	for name, testCase := range testCases {
-		testCase := testCase
 		t.Run(name, func(t *testing.T) {
 			t.Parallel()
 
@@ -152,7 +151,6 @@ func Test_getNextBlock(t *testing.T) {
 	}
 
 	for name, testCase := range testCases {
-		testCase := testCase
 		t.Run(name, func(t *testing.T) {
 			t.Parallel()