Implement database rotation with n days retention (#2)

- Automatically erase history, keep as separate timestamped files.
- Full history may be recovered by concatenation of the files.
- Only applied at database opening time.
- Enable by Kanta(retention=...), use with care (experimental feature).

pyproject.toml

@@ -17,7 +17,6 @@ readme = "README.md"
 requires-python = ">=3.11"
 dependencies = [
     "blake3>=1.0.8",
-    "jsondiff>=2.2.1",
     "msgspec>=0.20.0",
 ]
 
@@ -30,10 +29,12 @@ bin = [
 ]
 
 [project.urls]
+Homepage = "https://vasanko.com/coders/kanta"
 Repository = "https://git.zi.fi/LeoVasanko/kanta"
 
 [dependency-groups]
 dev = [
+    "jsondiff>=2.2.1",
     "pytest>=9.0.2",
     "pytest-asyncio>=1.3.0",
 ]