Update to collections module structure to support python 3.9+

[jerdmanGH]

Update to the collections module import to support newer versions of python where the MutableMapping module has changed. Tested with Python 3.6, 3.8, 3.9, and 3.10 - all tests pass successfully in all versions.

[AsmisAlan]

please, can u merge this pr ?

[infinidem]

Agreed, this should be merged to support Python 3.8+, currently on 3.11.3

[SofyaSasnavik-sm]

Please merge it, really need it to use it with python 3.11

[jakobkogler]

@infinidem @SofyaSasnavik-sm Feel free to switch to library https://github.com/dataclass-mapper/dataclass-mapper/. It has pretty much the same features as object-mapper, and it is maintained (by me :smile: ).