switch testing of fx and equity instruments to doctests.

improve format of examples for credit instruments.

Use doctests for testing credit instruments.

Use doctests for testing order classes.

Ease import of order classes.

Add timestamp to orders.

improve import of the different instruments.

run all tox actions on github

Update attrs usage + improve tox setup + replace lint with ruff + python 3.11 support

Update dependencies

Merge pull request #4 from TradingPy/dependabot/pip/notebook-6.4.12

Bump notebook from 6.4.10 to 6.4.12

Update README.md

Update README.md

Update README.md