fix(github): address review findings on client.go

- Use net/url.Parse for HTTPS scheme check (case-insensitive)
- Guard SetHTTPClient against nil (restores default 30s client)
- Rename 'url' param to 'reqURL' in doRequest/doGet for clarity
- Return error when response exceeds maxResponseBytes instead of
  silently truncating

Finding #1 (Bearer auth scheme) intentionally kept: GitHub REST API
officially supports and recommends Bearer for all token types.
See: https://docs.github.com/en/rest/authentication/authenticating-to-the-rest-api

github/client_test.go

@@ -282,8 +282,7 @@ func TestDoRequest_SetsUserAgentHeader(t *testing.T) {
 }
 
 func TestDoRequest_LimitsResponseBody(t *testing.T) {
-	// Verify that response body reading is actually bounded by maxResponseBytes.
-	// Use a small custom limit to avoid allocating 10 MiB in tests.
+	// Verify that oversized responses return an error rather than silently truncating.
 	bigBody := strings.Repeat("x", maxResponseBytes+1024)
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(200)
@@ -293,13 +292,12 @@ func TestDoRequest_LimitsResponseBody(t *testing.T) {
 
 	c := NewClient("token", srv.URL, AllowInsecureHTTP())
 	c.SetHTTPClient(srv.Client())
-	body, err := c.doGet(context.Background(), srv.URL+"/test")
-	if err != nil {
-		t.Fatalf("unexpected error: %v", err)
+	_, err := c.doGet(context.Background(), srv.URL+"/test")
+	if err == nil {
+		t.Fatal("expected error for oversized response body")
 	}
-	// LimitReader should cap the body at maxResponseBytes
-	if len(body) > maxResponseBytes {
-		t.Errorf("expected body <= %d bytes, got %d", maxResponseBytes, len(body))
+	if !strings.Contains(err.Error(), "exceeded") {
+		t.Errorf("expected truncation error, got: %v", err)
 	}
 }
 
@@ -384,3 +382,14 @@ func TestDoRequest_AllowsHTTPWithInsecureOption(t *testing.T) {
 		t.Errorf("unexpected body: %s", body)
 	}
 }
+
+func TestSetHTTPClient_NilRestoresDefault(t *testing.T) {
+	c := NewClient("token", "https://api.github.com")
+	c.SetHTTPClient(nil)
+	if c.httpClient == nil {
+		t.Fatal("expected non-nil httpClient after SetHTTPClient(nil)")
+	}
+	if c.httpClient.Timeout != 30*time.Second {
+		t.Errorf("expected 30s timeout, got %v", c.httpClient.Timeout)
+	}
+}