[Draw][Breakpoints] Place and route graphical breakpoints updates

[haydar-c]

The updates in this PR are:

• Added early validation of breakpoint expressions when the user sets them. Invalid expressions are now rejected immediately with an “Invalid Expression” message, preventing crashes later.
• Fixed router iteration breakpoints: previously, when a router_iter condition was met, the debugger stopped on every net in that iteration. Now, it stops once per router iteration, and will only stop again when the condition is met in a future iteration.
• Fixed a typo in the breakpoint pop-up message.

Related Issue
#3284

[vaughnbetz]

LGTM. I assume the user gets a message of some sort if he/she types in an invalid expression -- is that correct?

[haydar-c]

Yes, exactly. When the user tries to set an invalid expression, we run an early validity check, and if it fails, a pop-up window is shown with the message “Invalid expression.” This prevents the expression from being added and avoids a crash later on.

[vaughnbetz]

Thanks!