feat: add overflow option to Pin widget to allow content beyond boundaries

[john-basilio]

Adds an overflow bool field to the Pin widget with a corresponding .overflow() builder method.

By default, Pin subtracts its position from the available layout space, which causes content to be clipped or repositioned when near the boundaries of its container The images below demonstrates it:

Here's what the node box and the text should look, consistently.

Here's what it looks like with the current Pin.

With .overflow(true), it skips this subtraction, giving the content the full available space regardless of position.

This is useful for infinite canvas or free-form layout scenarios where pinned content should be able to move freely without being constrained by its screen position.

You can check out my repo's canvas.rs where pin() was used.