feat: Remove deprecated test files and enhance documentation for version 3.3.0 "Nexus Infinitum"

- Deleted obsolete test files: test_mime.go, test_mime_integration.go, and xmpp_client_upload_diagnosis.ipynb.
- Updated README.md to reflect the new version 3.3.0 "Nexus Infinitum" and its features.
- Added comprehensive release notes for version 3.3.0 detailing major enhancements and installation instructions.
- Introduced cleanup script to remove development artifacts while preserving production files.

test-minimal.toml

@@ -1,14 +0,0 @@
-[server]
-listen_address = "8080"
-storage_path = "./test-uploads"
-network_events = true
-
-[security]
-secret = "supersecret-hmac-key-minimum-16-chars"
-
-[logging]
-level = "info"
-file = ""
-
-[network_resilience]
-enabled = true