fix: add default value for access token in HttpClient init

[lukasthalerINNIO]

Summary

0.8.12 introduced a new access_token parameter to the clickhouse_connect.driver.HttpClient class that is marked as Optional[str] but has no default value. It is properly defaulted in create_client, but if you directly create an instance of HttpClient in 0.8.12, it fails due to the missing new argument

This PR adds a None default value to the HttpClient __init__ to mirror create_client and fix the issue

Checklist

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• A human-readable description of the changes was provided to include in CHANGELOG: Set default value for the optional access_token parameter of the HttpClient.__init__ method

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[genzgd]

Thanks for the fix! Do you need a release with this change immediately?

[lukasthalerINNIO]

A quick release would be much appreciated. We use uncapped clickhouse-connect dependencies a fair bit and all new builds are crashing due to this. I've put out a PSA to the team, but a new release would make our lives a lot easier

[genzgd]

I've pushed a PyPi release. Just a gentle reminder that the driver is still beta and it's recommended to use a specific, tested version for production workloads.