feat(src): Move core implementation files to src/ directory

src/cost_tracker.py

@@ -0,0 +1,28 @@
+import re
+
+# Pricing per 1M tokens in USD
+MODEL_PRICING = [
+    (r"gemini-2\.5-flash-lite", {"input_per_mtok": 0.075, "output_per_mtok": 0.30}),
+    (r"gemini-2\.5-flash", {"input_per_mtok": 0.15, "output_per_mtok": 0.60}),
+    (r"gemini-3-flash-preview", {"input_per_mtok": 0.15, "output_per_mtok": 0.60}),
+    (r"gemini-3\.1-pro-preview", {"input_per_mtok": 3.50, "output_per_mtok": 10.50}),
+    (r"claude-.*-sonnet", {"input_per_mtok": 3.0, "output_per_mtok": 15.0}),
+    (r"claude-.*-opus", {"input_per_mtok": 15.0, "output_per_mtok": 75.0}),
+    (r"deepseek-v3", {"input_per_mtok": 0.27, "output_per_mtok": 1.10}),
+]
+
+def estimate_cost(model: str, input_tokens: int, output_tokens: int) -> float:
+    """
+    Estimate the cost of a model call based on input and output tokens.
+    Returns the total cost in USD.
+    """
+    if not model:
+        return 0.0
+        
+    for pattern, rates in MODEL_PRICING:
+        if re.search(pattern, model, re.IGNORECASE):
+            input_cost = (input_tokens / 1_000_000) * rates["input_per_mtok"]
+            output_cost = (output_tokens / 1_000_000) * rates["output_per_mtok"]
+            return input_cost + output_cost
+            
+    return 0.0