tests/basics: Split out specific bytearray tests to separate files.

So they can be automatically skipped if bytearray is not enabled.

tests/basics/bytes_add.py

@@ -1,8 +1,6 @@
 # test bytes + other
 
 print(b"123" + b"456")
-print(b"123" + bytearray(2))
 
 print(b"123" + b"") # RHS is empty, can be optimised
 print(b"" + b"123") # LHS is empty, can be optimised
-print(b"" + bytearray(1)) # LHS is empty but can't be optimised