fix word sticking together, finally 🤯

[WilsonLe]

Testing steps to ensure it's fixed:

• Obtain a message that has the following format "A bunch of text, 🥲 then emojis in between, 🤯 then more texts". A reliable method to achieve this kind of message is as follow:
  • Create chat group
  • Invite bot in discussion mode
  • React the ⏩ icon in bot join message
  • It should send a message with the desired format
• Click on the message to trigger practice activities
• The message should not be sticking together

[WilsonLe]

Dev notes:

🚀 <-- escaping this is something like "\a123\a321"
we were substring-ing the pair \a123\a321 into 2 so called strings \a123 and \a321, which make flutter freaks out

I installed a package that checks if we are substringing a pair of those that we are not supposed to. It's similar to python's grapheme package but for flutter