fix(dotnet-sdk): Fix broken rate limit handling

[Hawxy]

Description

This unhelpfully deadlocked my test pipeline today. This code hasn't been touched for 3 years and has always been broken as far as I can tell. The tests also made the incorrect assumption about the header shape.

In the test suite, change the header configuration to:
response.Headers.Add(RateLimitParser.RateLimitHeader.LimitResetIn, DateTimeOffset.UtcNow.AddSeconds(10).ToUnixTimeSeconds().ToString());

And the assertion to:
Assert.InRange(error.ResetInMs!.Value, 0, 10000);

References

Closes openfga/dotnet-sdk#76

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

[linux-foundation-easycla]

• ✅login: Hawxy / (a111abb)

The committers listed above are authorized under a signed CLA.

[rhamzeh]

Thanks @Hawxy!

If you don't mind - will do some changes to your PR as we want to move from supporting these old headers to supporting the standard Retry-After header.

Related issues:

• Support the Retry-After header #495