tests: Split out those tests requiring float and import.

Tests in basics (which should probably be renamed to core) should not
rely on float, or import any non-built-in files.  This way these tests
can be run when those features are not available.

All test in basics now pass on the pyboard using stmhal port, except for
string-repr which has some issues with character hex printing.

tests/basics/types2.py

@@ -9,4 +9,6 @@ print(int == int)
 print(int != list)
 
 d = {}
-d[int] = float
+d[int] = list
+d[list] = int
+print(len(d))