feat: Add multi-threaded concurrent download support

- Add ThreadPoolExecutor for parallel attachment downloads
- Add --max-workers parameter to control concurrency (default: 5)
- Implement thread-safe logging with Lock mechanism
- Refactor _do_download to use concurrent.futures
- Add _download_single_file and _download_single_link helper functions
- Update CLAUDE.md with multi-threading documentation

Performance improvements:
- File attachments (OData) now download in parallel
- Link attachments (Scrapling) now download in parallel
- Configurable worker threads for different network conditions

CLAUDE.md

@@ -19,7 +19,7 @@ This is a SAP C4C (Cloud for Customer) attachment downloader toolkit that retrie
 2. Fetches ServiceRequest attachments via OData endpoints:
    - `/sap/c4c/odata/v1/c4codata` - Standard C4C OData API
    - `/sap/c4c/odata/cust/v1/custticketapi` - Custom ticket API
-3. Downloads two types of attachments:
+3. Downloads two types of attachments using **multi-threaded concurrent downloads**:
    - **File attachments** (CategoryCode=2): Downloaded via OData `$value` endpoint
    - **Link attachments** (CategoryCode=3): External Salesforce links scraped using Scrapling + Playwright
 4. Handles XIssueItem-level attachments via `BO_XSRIssueItemAttachmentFolder`
@@ -30,6 +30,11 @@ This is a SAP C4C (Cloud for Customer) attachment downloader toolkit that retrie
 - `scrapling[all]` - Web scraping framework with stealth capabilities
 - `playwright` - Browser automation for downloading Salesforce attachments
 
+**Performance features:**
+- Multi-threaded concurrent downloads (default: 5 threads, configurable via `--max-workers`)
+- Thread-safe output logging with lock mechanism
+- Parallel processing of both file and link attachments
+
 **Output modes:**
 - Human-readable console output (default)
 - JSON mode (`--json`) for programmatic consumption
@@ -71,6 +76,14 @@ python sap-c4c-AttachmentFolder.py \
   --password xxx \
   --ticket 24588
 
+# Download with custom thread count (default: 5)
+python sap-c4c-AttachmentFolder.py \
+  --tenant https://xxx.c4c.saphybriscloud.cn \
+  --user admin \
+  --password xxx \
+  --ticket 24588 \
+  --max-workers 10
+
 # Download with DSM upload
 python sap-c4c-AttachmentFolder.py \
   --tenant https://xxx.c4c.saphybriscloud.cn \