Add pytest test suite for core functionality

- Add pytest and pytest-asyncio to dev-reqs.txt
- Add tests for Router symbol detection regex (stocks and crypto patterns)
- Add tests for Symbol, Stock, and Coin class construction
- Add tests for rate_limited decorator functionality
- Add conftest.py with path setup and test environment variables

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/conftest.py

@@ -0,0 +1,15 @@
+"""Pytest configuration and fixtures."""
+
+import sys
+import os
+from pathlib import Path
+
+# Add the project root to Python path so we can import modules
+project_root = Path(__file__).parent.parent
+sys.path.insert(0, str(project_root))
+
+# Set environment variables for testing
+os.environ.setdefault("TELEGRAM", "test_token")
+os.environ.setdefault("DISCORD", "test_token")
+os.environ.setdefault("MARKETDATA", "test_token")
+os.environ.setdefault("STRIPE", "test_token")