chore: do not use sentinel errors when unneeded

- main reason being it's a burden to always define sentinel errors at global scope, wrap them with `%w` instead of using a string directly
- only use sentinel errors when it has to be checked using `errors.Is`
- replace all usage of these sentinel errors in `fmt.Errorf` with direct strings that were in the sentinel error
- exclude the sentinel error definition requirement from .golangci.yml
- update unit tests to use ContainersError instead of ErrorIs so it stays as a "not a change detector test" without requiring a sentinel error

internal/natpmp/rpc_test.go

@@ -20,20 +20,17 @@ func Test_Client_rpc(t *testing.T) {
 		initialConnectionDuration time.Duration
 		exchanges                 []udpExchange
 		expectedResponse          []byte
-		err                       error
 		errMessage                string
 	}{
 		"gateway_ip_unspecified": {
 			gateway:    netip.IPv6Unspecified(),
 			request:    []byte{0, 0},
-			err:        ErrGatewayIPUnspecified,
 			errMessage: "gateway IP is unspecified",
 		},
 		"request_too_small": {
 			gateway:                   netip.AddrFrom4([4]byte{127, 0, 0, 1}),
 			request:                   []byte{0},
 			initialConnectionDuration: time.Nanosecond, // doesn't matter
-			err:                       ErrRequestSizeTooSmall,
 			errMessage: `checking request: message size is too small: ` +
 				`need at least 2 bytes and got 1 byte\(s\)`,
 		},
@@ -53,7 +50,6 @@ func Test_Client_rpc(t *testing.T) {
 			exchanges: []udpExchange{
 				{request: []byte{0, 1}, close: true},
 			},
-			err: ErrConnectionTimeout,
 			errMessage: "connection timeout: failed attempts: " +
 				"read udp 127.0.0.1:[1-9][0-9]{0,4}->127.0.0.1:[1-9][0-9]{0,4}: i/o timeout \\(try 1\\)",
 		},
@@ -66,7 +62,6 @@ func Test_Client_rpc(t *testing.T) {
 				request:  []byte{0, 0},
 				response: []byte{1},
 			}},
-			err: ErrResponseSizeTooSmall,
 			errMessage: `checking response: response size is too small: ` +
 				`need at least 4 bytes and got 1 byte\(s\)`,
 		},
@@ -80,7 +75,6 @@ func Test_Client_rpc(t *testing.T) {
 				request:  []byte{0x0, 0x2, 0x0, 0x0, 0x0, 0x7b, 0x1, 0xc8, 0x0, 0x0, 0x4, 0xb0},
 				response: []byte{0, 1, 2, 3}, // size 4
 			}},
-			err: ErrResponseSizeUnexpected,
 			errMessage: `checking response: response size is unexpected: ` +
 				`expected 5 bytes and got 4 byte\(s\)`,
 		},
@@ -94,7 +88,6 @@ func Test_Client_rpc(t *testing.T) {
 				request:  []byte{0x0, 0x2, 0x0, 0x0, 0x0, 0x7b, 0x1, 0xc8, 0x0, 0x0, 0x4, 0xb0},
 				response: []byte{0x1, 0x82, 0x0, 0x0, 0x0, 0x14, 0x4, 0x96, 0x0, 0x7b, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0},
 			}},
-			err:        ErrProtocolVersionUnknown,
 			errMessage: "checking response: protocol version is unknown: 1",
 		},
 		"unexpected_operation_code": {
@@ -107,7 +100,6 @@ func Test_Client_rpc(t *testing.T) {
 				request:  []byte{0x0, 0x2, 0x0, 0x0, 0x0, 0x7b, 0x1, 0xc8, 0x0, 0x0, 0x4, 0xb0},
 				response: []byte{0x0, 0x88, 0x0, 0x0, 0x0, 0x14, 0x4, 0x96, 0x0, 0x7b, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0},
 			}},
-			err:        ErrOperationCodeUnexpected,
 			errMessage: "checking response: operation code is unexpected: expected 0x82 and got 0x88",
 		},
 		"failure_result_code": {
@@ -120,7 +112,6 @@ func Test_Client_rpc(t *testing.T) {
 				request:  []byte{0x0, 0x2, 0x0, 0x0, 0x0, 0x7b, 0x1, 0xc8, 0x0, 0x0, 0x4, 0xb0},
 				response: []byte{0x0, 0x82, 0x0, 0x11, 0x0, 0x14, 0x4, 0x96, 0x0, 0x7b, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0},
 			}},
-			err:        ErrResultCodeUnknown,
 			errMessage: "checking response: result code: result code is unknown: 17",
 		},
 		"success": {
@@ -153,9 +144,6 @@ func Test_Client_rpc(t *testing.T) {
 				testCase.request, testCase.responseSize)
 
 			if testCase.errMessage != "" {
-				if testCase.err != nil {
-					assert.ErrorIs(t, err, testCase.err)
-				}
 				assert.Regexp(t, "^"+testCase.errMessage+"$", err.Error())
 			} else {
 				assert.NoError(t, err)