Link Detection causing CPU usage to spike

User reported when using Simplenote, specifically on a note which contains 5 thousand email addresses, their CPU usage spikes to 99%.

They have no issues working on the same note on the Web app, Android and iOS

3537586-zen
They are on a macOS Catalina 10.15.7
MacBook pro 15" 2017
Processor 2.9GH quadcore intel core i7
ram 16GB

The user has not confirmed Simplenote version, I have just asked them to provide that.

### Expected

User would be able to work on the tickets without spiking CPU usage

### Observed
when using Simplenote, specifically on a note which contains 5 thousand email addresses, their CPU usage spikes to 99%.

### Reproduced

I was not able to reproduce it since I don't own a MacBook, but @rezzap was able to by creating a new note and adding several email links.

macOS 10.15.7, Simplenote 2.4, macBook Pro 13", 2019 2.8 Ghz Quad-Core Intel Core i7

***(Optional)*** If applicable, add screenshots, animations, or videos to help illustrate your problem.

Screenshots and more details are on the ticket.

Start by investigating Simplenote for macOS's link-detection behavior with a note containing thousands of email addresses. Use the reported Simplenote 2.4 and macOS 10.15.7 reproduction details as a baseline, then confirm that editing the note no longer drives CPU usage to 99%.

Written by the indexing model from the issue text.