fix(core): track pre-edit selection via beforeinput to stop desync

[artnikbrothers]

Fast typing (or holding Backspace) can revert or duplicate characters. Root cause:

• The pre-edit selection needed to classify each input event (insert vs delete, and the edited range) was cached only by a self-rescheduling setTimeout(0) poll.
• Browsers throttle nested zero-delay timers to a ~4ms floor, so under fast typing (or extra work per keystroke, e.g. a form library revalidating on change) the poll falls behind the real cursor position.
• Separately, a plain element.value = write - e.g. a controlled component re-rendering with a reformatted value - moves the cursor to the end without firing input or updating the cached selection.
• Either way the cached selection goes stale, so the next keystroke's addedValue slice spans the wrong range and splices text back at the wrong position - producing the reverted/duplicated characters.

Fix: capture the pre-edit selection from the beforeinput event instead. It fires synchronously right before the browser applies an edit, so it always reflects the real DOM selection at that instant, including a cursor already moved by a prior controlled re-render. The existing setTimeout poll stays in place as a fallback for cases beforeinput doesn't cover (autofill, or a pure cursor move with no edit).

Fixes #59

[artnikbrothers]

Hi @GoncharukBro, any chance we can review this PR and if all good release it? we have a problem in our applications because of this issue, and would really appreciate if we can fix it