feat: type hinting improvements

[evansims]

Description

This pull request is a first pass at type hinting improvements I'm making to the SDK. This first pass addresses errors in the existing type hints and ensures our client models are fully typed and hinted appropriately.

This pull request adds the mypy static type linter to our build process and an initial configuration for it to the pyproject.toml file. Note that there are a few commented-out flags; I intend to enable these with future passes.

References

This PR is a step towards addressing #109, but further work is required before we can call that closed.

Generated from openfga/sdk-generator#480

Review Checklist

• I have clicked on "allow edits by maintainers".
• I have added documentation for new/changed functionality in this PR or in a PR to openfga.dev [Provide a link to any relevant PRs in the references section above]
• The correct base branch is being used, if not main
• I have added tests to validate that the change in functionality is working as expected

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 84.38819% with 148 lines in your changes missing coverage. Please review.

Project coverage is 70.38%. Comparing base (c1339ea) to head (894509a).

Files with missing lines	Patch %	Lines
openfga_sdk/help.py	0.00%	43 Missing ⚠️
openfga_sdk/telemetry/configuration.py	65.51%	30 Missing ⚠️
openfga_sdk/telemetry/attributes.py	75.00%	15 Missing ⚠️
openfga_sdk/telemetry/metrics.py	55.17%	13 Missing ⚠️
openfga_sdk/rest.py	88.00%	6 Missing ⚠️
openfga_sdk/sync/rest.py	89.79%	5 Missing ⚠️
openfga_sdk/client/models/assertion.py	76.47%	4 Missing ⚠️
...a_sdk/client/models/client_batch_check_response.py	75.00%	4 Missing ⚠️
openfga_sdk/client/models/batch_check_item.py	89.28%	3 Missing ⚠️
openfga_sdk/client/models/write_single_response.py	80.00%	3 Missing ⚠️
... and 15 more

❌ Your project status has failed because the head coverage (70.38%) is below the target coverage (80.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #167      +/-   ##
==========================================
+ Coverage   69.58%   70.38%   +0.79%     
==========================================
  Files         135      134       -1     
  Lines       10864    10794      -70     
==========================================
+ Hits         7560     7597      +37     
+ Misses       3304     3197     -107     

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