fix: ensure `max_parallel_requests` is an `int` value in `batch_check`

[evansims]

Description

This change addresses a bug where batch_check typing was configured to only accept string values as part of the options dict; however, the max_parallel_requests option (later used by the ThreadPoolExecutor) requires this to be an integer value.

This PR:

• Updates the method signature to accept str | int as values for the dict.
• Adds a check to determine if max_parallel_requests was passed as an str or int.
  • if it was passed as a str, and Python verifies the string represents a numerical value (using isdigit()), then the value is cast to an int and used.
  • If it was passed as an int, the value is used.

References

closes #128

Review Checklist

• [x] 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]
• [x] 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 75.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 69.16%. Comparing base (e2ce832) to head (a118952).

Files with missing lines	Patch %	Lines
openfga_sdk/client/client.py	75.00%	1 Missing :warning:
openfga_sdk/sync/client/client.py	75.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #132 +/- ## ========================================== - Coverage 69.16% 69.16% -0.01% ========================================== Files 121 121 Lines 9982 9988 +6 ========================================== + Hits 6904 6908 +4 - Misses 3078 3080 +2 ```

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