Update mypy to 0.981 to support cross-platform development

[perplover]

Make this project cross-compatible with linux development. This still keeps the project compatible for Python 3.8+

Previously, the error was:

Installing the current project: hyperliquid-python-sdk (0.7.1)
poetry run mypy --install-types --non-interactive ./
venv/lib/python3.10/site-packages/eth_utils/__init__.py:1: note: In module imported here,
./hyperliquid/utils/signing.py:5: note: ... from here:
venv/lib/python3.10/site-packages/pkg_resources-stubs/__init__.pyi:329:79: error: Positional-only parameters are only supported in Python 3.8
and greater  [syntax]
        def __init__(self, dist: Distribution, req: Requirement, /, *args: object) -> None: ...
                                                                                  ^
Found 1 error in 1 file (errors prevented further checking)
make: [Makefile:11: install] Error 2 (ignored)

Updating the package to resolve positional arguments:

Installing the current project: hyperliquid-python-sdk (0.7.1)
poetry run mypy --install-types --non-interactive ./
Success: no issues found in 36 source files

Link to all mypy patches in between version upgrades:

• https://mypy-lang.blogspot.com/2022/09/mypy-0981-released.html
• https://mypy-lang.blogspot.com/2022/07/mypy-0971-released.html
• https://mypy-lang.blogspot.com/2022/05/mypy-0960-released.html
• https://mypy-lang.blogspot.com/2022/04/mypy-0950-released.html
• https://mypy-lang.blogspot.com/2022/03/mypy-0940-released.html

[minghinmatthewlam]

I also ran into this #57

[traderben]

Is there a reason for this PR given that #57 is already in review and seems to make approximately the same change?

[perplover]

happy to merge them or @minghinmatthewlam if you want to remove the python3.10+ requirements I can close this PR