Added greenbutton_objects

[AdamFinkle]

Added greenbutton_objects to parse Green Button XML electric and natural gas bills and wrote tests for the same, pydantic models for the same, and tests for the pydantic models.

[thadk]

Ah, at least in the 4th failing test in javascript, to make that pass Test, build, & deploy / ⚡ Heat-Stack - Vitest pyodide.test.ts (pull_request) we need to add new code to download and install the greenbutton_objects library in javascript python aka pyodide, sort of the equivalent of requirements.txt

[AdamFinkle]

I have corrected the linting error and the first MyPy error part, which was a typing signature mismatch. The second part of the MyPy error seems to involve the lack of typing in greenbutton_objects, which I could correct in one of three ways:

1. Add type hints to greenbutton_objects
2. Generate stubs for greenbutton_objects, potentially with the automatic stub generator of mypy, perhaps requiring these stubs to be installed into HEAT separately
3. Suppress this warning by suffixing the relevant greenbutton_python import statement with # type: ignore

I have chosen option three for now and made type hinting an issue for later. The pytest failure doesn't happen on my end and seems to be an off-by-one error, which may be caused by a difference between the GitHub pytest environment and the one on my end, where I have carefully checked the expected result saved in the .txt file and found that it matches the code.

[AdamFinkle]

All but the last two tests now pass. Trying additional National Grid .csv and .xml files does not yet work.