fix(web): fix Future already completed error when connectTimeout was set

[AlexV525]

Picked from cfug/dio#1550

fix Future already completed error when connectTimeout was set.

New Pull Request Checklist

• I have read the Documentation
• I have searched for a similar pull request in the project and found none
  • Fix for "Future already completed" error in web #1496
  • Browser adapter time out #1470
• I have updated this branch with the latest develop to avoid conflicts (via merge from master or rebase)
• I have added the required tests to prove the fix/feature I am adding
• I have updated the documentation (if necessary)
• I have run the tests and they pass

This merge request fixes / refers to the following issues:

• [web] Frequent Bad state: Future already completed #1536
• "Future already completed" error in web #1497

Pull Request Description

Use Timer instead of Future.delay to implement connectTimeout on Web.