Add Safe File Handling with QuantifyingException

[Opsmithe]

Fixes

• Fixes Add shared function to open data files and handle errors #251 by @Goziee-git

Problem

Process and report scripts fail with cryptic FileNotFoundError exceptions when required data files don't exist, providing unhelpful error messages to users.

Solution

Added safe_open_file() function to shared.py that validates file existence before operations and converts FileNotFoundError to meaningful QuantifyingException messages.

Changes

• Added safe_open_file() function in scripts/shared.py
• Updated all process scripts to use safe file validation:
  • scripts/2-process/gcs_process.py (3 calls)
  • scripts/2-process/github_process.py (1 call)
• Updated all report scripts to use safe file validation:
  • scripts/3-report/gcs_report.py (9 calls)
  • scripts/3-report/github_report.py (2 calls)

Before/After

Before:

FileNotFoundError: [Errno 2] No such file or directory: 'github_1_count.csv'

After:

QuantifyingException: Cannot process GitHub count data file: github_1_count.csv does not exist

Testing

• All static analysis checks pass (black, flake8, isort)
• Existing exception handling in scripts catches QuantifyingException
• Scripts exit gracefully with helpful error messages

Files Changed

• scripts/shared.py
• scripts/2-process/gcs_process.py
• scripts/2-process/github_process.py
• scripts/3-report/gcs_report.py
• scripts/3-report/github_report.py

Checklist

• I have read and understood the Developer Certificate of Origin (DCO), below, which covers the contents of this pull request (PR).
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• My pull request has a descriptive title (not a vague title like Update index.md).
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• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added or updated tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no
  visible errors.

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