Refactor Cart into checkerboard table

Closes: #173 (closed)

Removes clear all feature from: #233

This one improves focus behavior in the cart, moving cart items and deleting items from the cart.

clive/__private/ui/operations/cart.py

 from __future__ import annotations
 
+import contextlib
 from typing import TYPE_CHECKING
 
 from textual import on
 from textual.binding import Binding
 from textual.containers import Horizontal
+from textual.css.query import NoMatches
 from textual.message import Message
 from textual.widgets import Static
 
@@ -25,6 +27,7 @@ from clive.__private.ui.widgets.scrolling import ScrollablePart
 
 if TYPE_CHECKING:
     from textual.app import ComposeResult
+    from typing_extensions import Self
 
     from clive.models import Operation
 
@@ -69,6 +72,13 @@ class CartItem(CliveCheckerboardTableRow, CliveWidget):
             self.to_idx = to_idx
             super().__init__()
 
+    class Focus(Message):
+        """Message sent when other CartItem should be focused."""
+
+        def __init__(self, target_idx: int) -> None:
+            self.target_idx = target_idx
+            super().__init__()
+
     def __init__(self, operation_idx: int) -> None:
         self.__idx = operation_idx
         assert self.is_valid(), "During construction, index has to be valid"
@@ -96,12 +106,32 @@ class CartItem(CliveCheckerboardTableRow, CliveWidget):
     def is_valid(self) -> bool:
         return self.__idx < self.__operations_count
 
+    def focus(self, _: bool = True) -> Self:
+        if focused := self.app.focused:  # Focus the corresponding button as it was before
+            assert focused.id, "Previously focused widget has no id!"
+            with contextlib.suppress(NoMatches):
+                previous = self.get_child_by_id(focused.id)
+                if previous.focusable:
+                    previous.focus()
+                    return self
+
+        for child in reversed(self.children):  # Focus first focusable
+            if child.focusable:
+                child.focus()
+        return self
+
     def get_operation_index(self) -> str:
         return f"{self.__idx + 1}." if self.is_valid() else "?"
 
     def get_operation_name(self) -> str:
         return humanize_operation_name(self.operation) if self.is_valid() else "?"
 
+    def action_select_previous(self) -> None:
+        self.post_message(self.Focus(target_idx=self.__idx - 1))
+
+    def action_select_next(self) -> None:
+        self.post_message(self.Focus(target_idx=self.__idx + 1))
+
     def get_operation_details(self) -> str:
         return humanize_operation_details(self.operation) if self.is_valid() else "?"
 
@@ -188,8 +218,10 @@ class Cart(BaseScreen):
         with self.__scrollable_part:
             yield CartTable()
 
-    async def __rebuild_items(self, from_index: int = 0) -> None:
-        await self.query_one(CartTable).rebuild(starting_from_element=from_index, row_type=CartItem)
+    async def __rebuild_items(self, from_index: int = 0, to_index: int | None = None) -> None:
+        await self.query_one(CartTable).rebuild(
+            starting_from_element=from_index, ending_with_element=to_index, row_type=CartItem
+        )
 
     @on(CartItem.Delete)
     async def remove_item(self, event: CartItem.Delete) -> None:
@@ -205,7 +237,7 @@ class Cart(BaseScreen):
         self.app.world.profile_data.cart.swap(event.from_idx, event.to_idx)
         self.app.trigger_profile_data_watchers()
         start, end = (event.from_idx, event.to_idx) if event.from_idx < event.to_idx else (event.to_idx, event.from_idx)
-        await self.query_one(CartTable).rebuild(starting_from_element=start, ending_with_element=end, row_type=CartItem)
+        await self.__rebuild_items(from_index=start, to_index=end)
 
     def action_summary(self) -> None:
         self.app.push_screen(TransactionSummaryFromCart())