fix: catch context errors from http provider (celestiaorg#1160)

It seems from attempts to perform state sync that the light client is
not correctly detecting when the context gets cancelled or the deadline
is exceeded as the error is being wrapped

```
�[90m12:53PM�[0m �[32mINF�[0m error from light block request from primary, removing... �[36merror=�[0m�[31m"post failed: Post \"https://rpc-snapscale.lunaroasis.net:443\": context deadline exceeded"�[0m �[36mheight=�[0m354290 �[36mmodule=�[0mlight �[36mprimary=�[0m{}
```

This PR checks to see if `context deadline exceeded` is contained within
the error and then returns the actual context error

light/provider/http/http.go

@@ -160,6 +160,14 @@ OUTER_LOOP:
 				time.Sleep(backoffTimeout(uint16(attempt)))
 				continue
 
+			// NOTE: it seems like the context errors are being wrapped in a way that
+			// makes them hard to detect. For now, we just check the error string.
+			case strings.Contains(err.Error(), context.DeadlineExceeded.Error()):
+				return nil, context.DeadlineExceeded
+
+			case ctx.Err() != nil:
+				return nil, ctx.Err()
+
 			// context canceled or connection refused we return the error
 			default:
 				return nil, err
@@ -202,6 +210,14 @@ func (p *http) signedHeader(ctx context.Context, height *int64) (*types.SignedHe
 			time.Sleep(backoffTimeout(uint16(attempt)))
 			continue
 
+		// NOTE: it seems like the context errors are being wrapped in a way that
+		// makes them hard to detect. For now, we just check the error string.
+		case strings.Contains(err.Error(), context.DeadlineExceeded.Error()):
+			return nil, context.DeadlineExceeded
+
+		case ctx.Err() != nil:
+			return nil, ctx.Err()
+
 		// either context was cancelled or connection refused.
 		default:
 			return nil, err

light/provider/http/http_test.go

@@ -15,6 +15,7 @@ import (
 	lighthttp "github.com/cometbft/cometbft/light/provider/http"
 	rpcclient "github.com/cometbft/cometbft/rpc/client"
 	rpchttp "github.com/cometbft/cometbft/rpc/client/http"
+	ctypes "github.com/cometbft/cometbft/rpc/core/types"
 	rpctest "github.com/cometbft/cometbft/rpc/test"
 	"github.com/cometbft/cometbft/types"
 )
@@ -46,10 +47,9 @@ func TestProvider(t *testing.T) {
 	chainID := genDoc.ChainID
 
 	c, err := rpchttp.New(rpcAddr, "/websocket")
-	require.Nil(t, err)
+	require.NoError(t, err)
 
 	p := lighthttp.NewWithClient(chainID, c)
-	require.NoError(t, err)
 	require.NotNil(t, p)
 
 	// let it produce some blocks
@@ -82,6 +82,21 @@ func TestProvider(t *testing.T) {
 	require.Nil(t, lb)
 	assert.Equal(t, provider.ErrLightBlockNotFound, err)
 
+	// fetching with the context cancelled
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+	_, err = p.LightBlock(ctx, lower+3)
+	require.Error(t, err)
+	require.Equal(t, context.Canceled, err)
+
+	// fetching with the deadline exceeded (a mock RPC client is used to simulate this)
+	c2, err := newMockHTTP(rpcAddr)
+	require.NoError(t, err)
+	p2 := lighthttp.NewWithClient(chainID, c2)
+	_, err = p2.LightBlock(context.Background(), 0)
+	require.Error(t, err)
+	require.Equal(t, context.DeadlineExceeded, err)
+
 	// stop the full node and check that a no response error is returned
 	rpctest.StopTendermint(node)
 	time.Sleep(10 * time.Second)
@@ -91,3 +106,19 @@ func TestProvider(t *testing.T) {
 	require.Contains(t, err.Error(), "connection refused")
 	require.Nil(t, lb)
 }
+
+type mockHTTP struct {
+	*rpchttp.HTTP
+}
+
+func newMockHTTP(remote string) (*mockHTTP, error) {
+	c, err := rpchttp.New(remote, "/websocket")
+	if err != nil {
+		return nil, err
+	}
+	return &mockHTTP{c}, nil
+}
+
+func (m *mockHTTP) Validators(ctx context.Context, height *int64, page, perPage *int) (*ctypes.ResultValidators, error) {
+	return nil, fmt.Errorf("post failed: %w", context.DeadlineExceeded)
+}