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/float/float1.py

@@ -0,0 +1,16 @@
+# basic float
+x = 1 / 2
+print(x)
+
+print(1.0 // 2)
+print(2.0 // 2)
+
+try:
+    1.0 / 0
+except ZeroDivisionError:
+    print("ZeroDivisionError")
+
+try:
+    1.0 // 0
+except ZeroDivisionError:
+    print("ZeroDivisionError")