feat: add compression response field to SendResponse

- Add Compression dataclass with input_tokens, saved_tokens, and rate fields
- Add optional compression field to SendResponse for root-level compression data

Author: CLEMENTINATOR

edgee/__init__.py

@@ -68,10 +68,18 @@ class Usage:
     total_tokens: int
 
 
+@dataclass
+class Compression:
+    input_tokens: int
+    saved_tokens: int
+    rate: float
+
+
 @dataclass
 class SendResponse:
     choices: list[Choice]
     usage: Usage | None = None
+    compression: Compression | None = None
 
     @property
     def text(self) -> str | None: