Convert MODE constants to IntEnum

Convert the MODE_* constants to an IntEnum class for better type
safety, IDE support, and more descriptive string representations.

Changes:
- Created Mode IntEnum with AUTO, MMAP_EXT, MMAP, FILE, MEMORY, FD members
- Added comprehensive documentation for the Mode class and each member
- Maintained backward compatibility by exporting old-style constants
  (MODE_AUTO, MODE_FILE, etc.) as aliases to enum members
- Added __all__ to explicitly define the public API

Benefits:
- Better IDE autocomplete and type hints
- Descriptive repr: <Mode.FILE: 4> instead of just 4
- Access to .name and .value attributes
- Full backward compatibility (IntEnum is int-compatible)
- Modern Python 3.10+ idiom
- Inline documentation for each mode visible in source and IDEs

Backward compatibility: All existing code continues to work unchanged.
Both Mode.FILE and MODE_FILE can be used interchangeably, and all
numeric comparisons work as before since IntEnum is int-compatible.

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

Co-Authored-By: Claude <[email protected]>

Author: oschwald

HISTORY.rst

@@ -31,6 +31,13 @@ History
   including the ``node_byte_size`` and ``search_tree_size`` properties. Note:
   The C extension's Metadata class has always been readonly, so this change
   brings the pure Python implementation into consistency with the C extension.
+* MODE constants have been converted to an ``IntEnum`` (``maxminddb.const.Mode``).
+  The old constants (``MODE_AUTO``, ``MODE_FILE``, etc.) remain available for
+  backward compatibility and are now aliases to the enum members. This provides
+  better IDE support and type safety while maintaining full backward
+  compatibility. You can now use either ``Mode.FILE`` or ``MODE_FILE`` - both
+  work identically. Since ``IntEnum`` is int-compatible, existing code using
+  the constants will continue to work without modification.
 
 2.8.2 (2025-07-25)
 ++++++++++++++++++

maxminddb/const.py

@@ -1,8 +1,47 @@
 """Constants used in the API."""
 
-MODE_AUTO = 0
-MODE_MMAP_EXT = 1
-MODE_MMAP = 2
-MODE_FILE = 4
-MODE_MEMORY = 8
-MODE_FD = 16
+from enum import IntEnum
+
+
+class Mode(IntEnum):
+    """Database open modes.
+
+    These modes control how the MaxMind DB file is opened and read.
+    """
+
+    AUTO = 0
+    """Try MODE_MMAP_EXT, MODE_MMAP, MODE_FILE in that order. Default mode."""
+
+    MMAP_EXT = 1
+    """Use the C extension with memory map."""
+
+    MMAP = 2
+    """Read from memory map. Pure Python."""
+
+    FILE = 4
+    """Read database as standard file. Pure Python."""
+
+    MEMORY = 8
+    """Load database into memory. Pure Python."""
+
+    FD = 16
+    """Database is a file descriptor, not a path. This mode implies MODE_MEMORY."""
+
+
+# Backward compatibility: export both enum members and old-style constants
+MODE_AUTO = Mode.AUTO
+MODE_MMAP_EXT = Mode.MMAP_EXT
+MODE_MMAP = Mode.MMAP
+MODE_FILE = Mode.FILE
+MODE_MEMORY = Mode.MEMORY
+MODE_FD = Mode.FD
+
+__all__ = [
+    "Mode",
+    "MODE_AUTO",
+    "MODE_MMAP_EXT",
+    "MODE_MMAP",
+    "MODE_FILE",
+    "MODE_MEMORY",
+    "MODE_FD",
+]