Fix configuration.md ConfigValue references

Removes the documentation for a non-existent ConfigValue dataclass and replaces it with accurate documentation for the real third dataclass, ServerVersion (fields: version, commit). Clarifies that get_all() returns dict[str, str] rather than a dataclass.

Closes #134

Author: zeevdr

sdk/docs/configuration.md

@@ -204,21 +204,20 @@ All exceptions inherit from `DecreeError`:
 
 ## Return types
 
-All return types are frozen dataclasses:
+`get_all()` returns a plain `dict[str, str]` mapping field paths to their string
+values — not a dataclass. The other typed return values are frozen dataclasses:
 
 ```python
-@dataclass(frozen=True, slots=True)
-class ConfigValue:
-    field_path: str
-    value: str
-    checksum: str
-    description: str
-
 @dataclass(frozen=True, slots=True)
 class Change:
     field_path: str
     old_value: str | None
     new_value: str | None
     version: int
     changed_by: str
+
+@dataclass(frozen=True, slots=True)
+class ServerVersion:
+    version: str
+    commit: str
 ```