reversed "update" method in multi_cache to overwrite old values with new

[Trizalio]

If wrapped function can return dict with more keys, than required there is a case, in which new value will be replaced by old, example:

import asyncio
from typing import List, Dict

from aiocache import multi_cached


@multi_cached("ids", namespace="main")
async def foo(ids: List[int]) -> Dict[int, int]:
    biggest_value = max(ids)
    result = {id_: biggest_value for id_ in range(biggest_value + 1)}
    print(f'foo result: {result}')
    return result


async def amain():
    print(await foo(ids=[1]))
    print(await foo(ids=[0, 2]))
    print(await foo(ids=[0]))

if __name__ == "__main__":
    asyncio.run(amain())

will be printed:

foo result: {0: 1, 1: 1}
{0: 1, 1: 1}
foo result: {0: 2, 1: 2, 2: 2}
{0: 1, 1: 2, 2: 2}
{0: 1}

As we can see, on second call of foo value for 1 changed, but it was overwritten by cache value.

In my case i must return aggregated values based on values from two distinct bigdata storages. Based on requested keys i can predict future requests, so i'd like to preload values for predicted keys with keys passed to my funstion and save them all in aiocache

[argaen]

Thanks for this @Trizalio!

We would need to add tests in order to merge this

[codecov]

Codecov Report

Merging #489 (9981377) into master (a966f84) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #489   +/-   ##
=======================================
  Coverage   99.13%   99.13%           
=======================================
  Files          13       13           
  Lines        1043     1044    +1     
  Branches      116      116           
=======================================
+ Hits         1034     1035    +1     
  Misses          9        9           

Impacted Files	Coverage Δ
aiocache/decorators.py	100.00% <100.00%> (ø)

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[Dreamsorcerer]

Looks reasonable, but as mentioned, please add a test (after merging master). Test probably should go in tests/ut/test_decorators.py