Add __str__ and __repr__ for simple array

[tigercosmos]

Add str and repr for simple array. Currently, it only prints the memory address.

>>> import _modmesh as mm
>>> a = mm.SimpleArray(10, "int32")
>>> repr(a)
'<_modmesh.SimpleArray object at 0x7fb28deae270>'
>>> print(a)
<_modmesh.SimpleArray object at 0x7fb28deae270>

[yungyuc]

The two string representations of arrays need careful design. Once made available, the results will be widely used in test cases and go beyond our control.