Modernize codebase to use (and require) cocotb 1.5+

[imphil]

This PR contains three commits to update the codebase to use more of the features introduced with cocotb 1.5 and newer.

• Don't include Makefile.inc any more
• Use bus components from cocotb-bus

Finally, to ensure things continue to work:

• Test examples through tox (and in CI)