Making crc32c defalut for download

[shubhangi-google]

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closes: #<issue_number_goes_here>

[gemini-code-assist]

Code Review

This pull request changes the default verification method for file downloads from MD5 to CRC32C across the google-cloud-storage library and updates the corresponding tests. A review comment identifies an issue in project_anonymous_test.rb where the stubbed CRC32C value is set to a zero checksum ("AAAAAA==") instead of matching the actual file content ("yay!"), which will cause the download verification to fail.

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[thiyaguk09]

LGTM