Improve type annotations for Record types and Decoder

Convert RecordList and RecordDict from class-based type definitions to
explicit TypeAlias declarations. These types are only used for type
annotations and were never instantiated as actual classes, so using
TypeAlias makes their purpose more explicit and follows modern Python
typing conventions.

Add explicit type annotation to Decoder._type_decoder ClassVar. This
provides better type checking for the decoder function map by fully
specifying the callable signature.

These are internal changes with no user-visible effects.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: oschwald

maxminddb/decoder.py

@@ -10,13 +10,16 @@
 except ImportError:
     mmap = None  # type: ignore[assignment]
 
-
 from maxminddb.errors import InvalidDatabaseError
 
 if TYPE_CHECKING:
+    from collections.abc import Callable
+
     from maxminddb.file import FileBuffer
     from maxminddb.types import Record
 
+    DecoderFunc = Callable[["Decoder", int, int], tuple[Record, int]]
+
 
 class Decoder:
     """Decoder for the data section of the MaxMind DB."""
@@ -118,7 +121,7 @@ def _decode_utf8_string(self, size: int, offset: int) -> tuple[str, int]:
         new_offset = offset + size
         return self._buffer[offset:new_offset].decode("utf-8"), new_offset
 
-    _type_decoder: ClassVar = {
+    _type_decoder: ClassVar[dict[int, DecoderFunc]] = {
         1: _decode_pointer,
         2: _decode_utf8_string,
         3: _decode_double,

maxminddb/types.py

@@ -6,13 +6,10 @@
 
 Primitive: TypeAlias = AnyStr | bool | float | int
 
+RecordList: TypeAlias = list["Record"]
+"""RecordList is a type for lists in a database record."""
 
-class RecordList(list["Record"]):
-    """RecordList is a type for lists in a database record."""
-
-
-class RecordDict(dict[str, "Record"]):
-    """RecordDict is a type for dicts in a database record."""
-
+RecordDict: TypeAlias = dict[str, "Record"]
+"""RecordDict is a type for dicts in a database record."""
 
 Record: TypeAlias = Primitive | RecordList | RecordDict