Better column definitions. (#31)

* Better column definitions.

* Address review comments.

* Simplifies the code of `_build_column`.

* parametrized tests.

Author: joce

src/appui/enhanced_data_table.py

@@ -14,7 +14,7 @@
 import sys
 from dataclasses import KW_ONLY, dataclass
 from functools import total_ordering
-from typing import TYPE_CHECKING, Generic, TypeVar
+from typing import TYPE_CHECKING, ClassVar, Generic, TypeVar
 
 from rich.text import Text
 from textual.binding import BindingsMap
@@ -47,6 +47,8 @@
 class EnhancedTableCell:  # pragma: no cover
     """Rich-renderable table cell with an ordering key."""
 
+    default_justification: ClassVar[Justify] = Justify.RIGHT
+
     def __init__(
         self,
         sort_key: tuple[object, ...],