[Typing] Fix type stubs

[n-takumasa]

• Fix default args: especially set_default_units()
• Fix math operators: especially mul and div

NOTE

# master
# pip install git+https://github.com/python-quantities/python-quantities

from typing import reveal_type
import quantities as pq

distance = 42 * pq.metre
time = 17 * pq.second
velocity = distance / time
reveal_type(velocity)
# Static type: Type of "velocity" is "ndarray[Any, dtype[floating[_64Bit]]]"
# Runtime type is 'Quantity'

reveal_type(distance * 2)
# Static type: Type of "distance * 2" is "ndarray[Any, dtype[signedinteger[Any]]]"
# Runtime: ValueError

reveal_type(distance + 1)
# Static type: Type of "distance + 1" is "Quantity"

# this PR

from typing import reveal_type
import quantities as pq

distance = 42 * pq.metre
time = 17 * pq.second
velocity = distance / time
reveal_type(velocity)
# Static type: Type of "velocity" is "Quantity"
# Runtime type is 'Quantity'

reveal_type(distance * 2)
# Type of "distance * 2" is "Quantity"

reveal_type(distance + 1)
# Operator "+" not supported for types "Quantity" and "Literal[1]"

reveal_type(distance + time)  # should be error but cannot detect by static type now