feat(parsers): add SOAP API support for zakupki.gov.ru

- Add post() method to BaseHTTPClient for SOAP requests
- Update download_file() to support custom headers (for token)
- Add ZAKUPKI_TOKEN and PARSER_PROXIES settings
- Improve SOAP error parsing to show EIS error messages
- Update E2E tests to use token from settings
- Add data/ and .zed/ to gitignore

.gitignore

@@ -39,3 +39,5 @@ Thumbs.db
 # Backup files
 *.bak
 *.backupdata/
+data/
+.zed/