Doorkeeper API の504エラーに対するリトライ処理とタイムアウト設定を追加

## 変更内容

### 1. タイムアウト設定の追加 (lib/event_service/client.rb)
- 接続タイムアウト: 10秒
- 読み取りタイムアウト: 60秒
- 無限待機を防止

### 2. サーバーエラーのリトライ処理 (lib/event_service/providers/doorkeeper.rb)
- 502/503/504エラーを検出して自動リトライ
- Exponential backoff: 10秒 → 20秒 → 40秒
- 最大3回までリトライ
- group_id を含む詳細なエラーログ

### 3. 詳細なログ出力 (lib/statistics/tasks/doorkeeper.rb)
- どのDojoを処理中かを表示
- 取得成功時のイベント数を表示
- エラー発生時にDojo名とgroup_idを記録

## 動作確認

ローカル環境で以下のタスクを実行し、正常動作を確認：
- `bundle exec rails statistics:aggregation`
  - 51個のDojoを正常に処理
- `bundle exec rails upcoming_events:aggregation`
  - Connpass: 116イベント取得
  - Doorkeeper: 2箇所で504エラー発生 → リトライで成功

## テスト

全216テストが成功：
```
bundle exec rspec spec
216 examples, 0 failures
```

## 関連Issue

統計/地図スクリプトの504エラーに対応

Author: yasulab

lib/event_service/client.rb

@@ -14,7 +14,7 @@ def get(path, params)
     private
 
     def connection_for(endpoint, proxy)
-      Faraday.new(endpoint, proxy: proxy) do |f|
+      Faraday.new(endpoint, proxy: proxy, request: { open_timeout: 10, timeout: 60 }) do |f|
         f.response :logger if self.class.debug
 
         # faraday標準のJSONパーサーを使用

lib/event_service/providers/doorkeeper.rb

@@ -17,35 +17,48 @@ def search(keyword:)
         end
 
         # NOTE: since_at, until_at は DateTime で指定
-        def fetch_events(group_id:, since_at: @default_since, until_at: @default_until)
-          begin
-            params = {
-              page: 1,
-              since: since_at.utc.iso8601,
-              until: until_at.utc.iso8601
-            }
-            events = []
+        def fetch_events(group_id:, since_at: @default_since, until_at: @default_until, retry_count: 0)
+          params = {
+            page: 1,
+            since: since_at.utc.iso8601,
+            until: until_at.utc.iso8601
+          }
+          events = []
 
-            loop do
-              part = @client.get("groups/#{group_id}/events", params)
+          loop do
+            part = @client.get("groups/#{group_id}/events", params)
 
-              break if part.size.zero?
+            break if part.size.zero?
 
-              events.push(*part.map { |e| e[:event] })
+            events.push(*part.map { |e| e[:event] })
 
-              break if part.size < 25   # 25 items / 1 request
+            break if part.size < 25   # 25 items / 1 request
 
-              params[:page] += 1
-            end
-
-            events
-          rescue Faraday::ClientError => e
-            raise e unless e.response[:status] == 429
+            params[:page] += 1
+          end
 
+          events
+        rescue Faraday::ClientError => e
+          # 429: Rate Limit
+          if e.response[:status] == 429
             puts 'API rate limit exceeded.'
             puts "This task will retry in 60 seconds from now(#{Time.zone.now})."
             sleep 60
             retry
+          else
+            raise e
+          end
+        rescue Faraday::ServerError => e
+          # 502, 503, 504: Server errors
+          if [502, 503, 504].include?(e.response[:status]) && retry_count < 3
+            wait_time = 2 ** retry_count * 10  # Exponential backoff: 10, 20, 40 seconds
+            puts "Server error (#{e.response[:status]}) for group_id: #{group_id}."
+            puts "Retrying in #{wait_time} seconds... (attempt #{retry_count + 1}/3)"
+            sleep wait_time
+            fetch_events(group_id: group_id, since_at: since_at, until_at: until_at, retry_count: retry_count + 1)
+          else
+            puts "Failed to fetch events for group_id: #{group_id} after #{retry_count} retries."
+            raise e
           end
         end
       end

lib/statistics/tasks/doorkeeper.rb

@@ -18,6 +18,7 @@ def initialize(dojos, period)
       def run
         @dojos.each do |dojo|
           dojo.dojo_event_services.for(:doorkeeper).each do |dojo_event_service|
+            puts "  Fetching events for #{dojo.name} (group_id: #{dojo_event_service.group_id})"
             events = @client.fetch_events(**@params.merge(group_id: dojo_event_service.group_id))
             (events || []).compact.each do |e|
               next unless e[:group].to_s == dojo_event_service.group_id
@@ -31,6 +32,10 @@ def run
                                    participants: e[:participants],
                                    evented_at:   Time.zone.parse(e[:starts_at]))
             end
+            puts "    ✓ Successfully fetched #{events&.size || 0} events"
+          rescue => e
+            puts "    ✗ Failed to fetch events for #{dojo.name} (group_id: #{dojo_event_service.group_id}): #{e.message}"
+            raise e
           end
         end
       end