Micropython 1.24.1 compatibility fixes

[kdmukai]

Changes for MicroPython v1.24.1

• m_new_obj_var expects a new input var: var_field. See: b6a9778
• mp_obj_new_str_from_vstr removed an input var. See: 8a0ee5a
• STATIC macro changed to just static. See: decf8e6
• mp_obj_type_t.make_new removed. See: 94beeab
• mp_obj_new_str_from_vstr now checks for utf-8 decoding; return bytes instead via mp_obj_new_bytes_from_vstr to avoid UnicodeError exceptions.
• MP_REGISTER_MODULE now only expects 2 args so MODULE_HASHLIB_ENABLED is no longer relevant.

Misc:

• Update crypto/sha2.c to eliminate warnings about array sizes not matching declarations in crypto/sha.h
• Enable -O2 compiler performance optimizations.
• README fix for correct pbkdf2_hmac() input args.