Fix flyweight_with_metaclass sharing instances for different arguments

[Darkslayer3324j]

Problem

FlyweightMeta._serialize_params builds the pool key with "".join(map(str, args)) + str(kwargs) + cls.__name__. There is no separator and the type of each argument is lost, so different calls collide and the second one silently gets the first one's instance:

>>> Card2("1", "0") is Card2("10")
True      # should be False
>>> Card2(1) is Card2("1")
True      # should be False

The reverse also happens: Card2(a=1, b=2) and Card2(b=2, a=1) are not shared, because str(kwargs) depends on insertion order.

Fix

Use repr((cls.__name__, args, sorted(kwargs.items()))) as the key. It keeps argument boundaries and types, and is independent of keyword order. The key is still a string, so nothing else about the pool changes (the __main__ demo still passes).

Tests

patterns/structural/flyweight_with_metaclass.py had no tests (42% covered). I added tests/structural/test_flyweight_with_metaclass.py with cases for sharing, non-sharing, argument boundaries, argument types and kwarg order. Three of the five fail on master and all pass with the change. The repo's lint steps (flake8, isort, black --check, mypy, codespell) are clean and pytest tests patterns passes (136 passed).

Written with AI assistance (Claude Code); I reproduced the collisions above and ran the checks.