Fix mypy typing errors

Errors:

    src/textual_dev/previews/borders.py:65: error: Incompatible types in assignment (expression has type "tuple[str, str]", variable has type "Sequence[tuple[Literal['', 'ascii', 'none', 'hidden', 'blank', 'round', 'solid', 'thick', 'double', 'dashed', 'heavy', 'inner', 'outer', 'hkey', 'vkey', 'tall', 'panel', 'wide'], str | Color] | None] | tuple[Literal['', 'ascii', 'none', 'hidden', 'blank', 'round', 'solid', 'thick', 'double', 'dashed', 'heavy', 'inner', 'outer', 'hkey', 'vkey', 'tall', 'panel', 'wide'], str | Color] | None")  [assignment]
    tests/utilities/wait_for_predicate.py:29: error: Incompatible types in assignment (expression has type "float", variable has type "int")  [assignment]

Author: vlaci

src/textual_dev/previews/borders.py

@@ -1,6 +1,8 @@
+from typing import cast
 from textual.app import App, ComposeResult
 from textual.containers import Vertical
 from textual.css.constants import VALID_BORDER
+from textual.css.types import EdgeType
 from textual.widgets import Button, Label
 
 TEXT = """I must not fear.
@@ -60,7 +62,7 @@ def compose(self) -> ComposeResult:
     def on_button_pressed(self, event: Button.Pressed) -> None:
         self.text.border_title = event.button.id
         self.text.styles.border = (
-            event.button.id,
+            cast(EdgeType, event.button.id),
             self.stylesheet._variables["secondary"],
         )
 

tests/utilities/wait_for_predicate.py

@@ -20,7 +20,7 @@ async def wait_for_predicate(
         poll_delay_secs (float): The number of seconds to wait between each call to the
             predicate function.
     """
-    time_taken = 0
+    time_taken = 0.0
     while True:
         result = predicate()
         if result: