Test feat bigframes

[ohmayr]

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Fixes #<issue_number_goes_here> 🦕

[gemini-code-assist]

Code Review

This pull request re-enables doctests for the bigframes package by removing a temporary skip in the Nox configuration and introducing a new shell script to manage doctest execution. The Kokoro configuration was updated to use a new project ID and point to this script. Additionally, some system tests were updated to ignore data type checks during series comparisons. Feedback was provided regarding a hardcoded project ID in the new script that overrides the configuration settings.

[gemini-code-assist]

The GOOGLE_CLOUD_PROJECT is hardcoded to bigframes-testing, which overrides the value set in the Kokoro configuration file (.kokoro/presubmit/presubmit-doctest-bigframes.cfg). This makes the configuration change to precise-truck-742 ineffective. It is recommended to use a conditional assignment to allow the configuration to control the project ID while providing a sensible default.

Suggested change

	export GOOGLE_CLOUD_PROJECT="bigframes-testing"
	export GOOGLE_CLOUD_PROJECT="${GOOGLE_CLOUD_PROJECT:-bigframes-testing}"