Fix test failures

a. `DeprecationWarning: The 'warn' method is deprecated, use 'warning' instead`
Updated call in `bumble/smp.py`

b. `ModuleNotFoundError: No module named 'bumble.apps'`
Updated imports in `tests/import_test.py`

c. Added `pytest-html` for easier viewing of test results
Added package in `setup.cfg`, and hook in `tasks.py`

d. Updated workflows to use `invoke test`

This is a partial fix of #81

setup.cfg

@@ -65,6 +65,7 @@ build =
 test =
     pytest >= 6.2
     pytest-asyncio >= 0.17
+    pytest-html >= 3.2.0
     coverage >= 6.4
 development =
     invoke >= 1.4