Consolidate checks for completion file exists

[oree-xx]

Fixes

• Fixes Consolidate checks for completion file exists #271

Description

I merged the functions that checks for processed files in process script and the last entry in report script. The function check_completion_file_exists() now performs both task in shared.py.

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[TimidRobot]

please update to better support --quarter in the report scripts

[TimidRobot]

Please update all three report scripts per the comments below.

Please remember to test your changes. For example:

pipenv run ./scripts/3-report/gcs_report.py --quarter 2025Q3

Had you done so, you would have seen the error.

[TimidRobot]

good work, thank you!