Added requirements in preparation for Threema E2E and Keybase support

[caronc]

Description

Related issue (if applicable): #apprise/1570

New updates to the Threema Plugin allows for E2E Encryption Support

Checklist

• Documentation ticket created (if applicable): apprise-docs/30
• The change is tested and works locally.
• No commented-out code in this PR.
• No lint errors (use tox -e lint and optionally tox -e format).
• Test coverage added or updated (use tox -e qa).

Testing

Anyone can help test as follows:

# Clone the branch
git clone -b threema-requirements https://github.com/caronc/apprise-api.git
cd apprise-api

# Run the unit tests
tox -e test

# Alternatively, spin up the full stack with Docker
docker compose up

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (624381b) to head (a65043b).

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #314   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           13        13           
  Lines         1424      1424           
  Branches       254       254           
=========================================
  Hits          1424      1424           

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