Bigquery proxy support

[mansfieldj3]

Adds support for supplying a HTTP / HTTPS proxy to the bigquery hook using any of

1. connection form widgets
2. As a field in the hook itself as a string i.e. BigQueryHook(http_proxy="http://proxy:8080")
3. As part of the connection extras i.e. "http_proxy": "http://proxy:8080"

• closes: Google Cloud Connection support for non-environmental proxy #64278

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Generated-by: Claude Sonnet 4.6 following the guidelines

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[mansfieldj3]

As an FYI, when testing in my environment the code was reformatted by Ruff which considerably expands the number of changes, if this is an issue, please let me know and I'll revert this

[mansfieldj3]

Should be ready for review (assuming it passes the checks)