Merge pull request #166 from dapper91/dev

- union collection deserialization bug fixed.

Merge pull request #163 from dapper91/dev

- mypy plugin added. See https://pydantic-xml.readthedocs.io/en/latest/pages/misc.html#mypy.
- optional raw element bug fixed. See #158.

Merge pull request #151 from dapper91/dev

- validation errors provide the full path to the malformed field (including nested sub-models).
- error text contain the xml document source line where the error occurred (lxml parser only). See #150.

Merge pull request #147 from dapper91/dev

- nillable element support added.

Merge pull request #144 from dapper91/dev

Dev

Merge pull request #139 from dapper91/dev

- attributes with default namespace bug fixed.

Merge pull request #136 from dapper91/dev

- bool type encoding format changed from 'True' to 'true'. 
- None type encoding format changed from 'None' to ''.

Merge pull request #132 from dapper91/dev

- root model default value bug fixed.
- python 3.12 support added.

Merge pull request #122 from dapper91/dev

- raw element missing tail bug fixed. See #118.

Merge pull request #115 from dapper91/dev

- model validator 'before' mode support added.