Refactor to R package, test-first approach, documentation and snake_case formatting

[alisadeghiaghili]

This pull request restructures the banking log cleaner scripts into a formal, structured R package.

• Created standard R package folders (R/, tests/testthat/).
• Renamed all functions and parameters to standard snake_case.
• Annotated code with roxygen2 documentation containing parameter descriptions, returns, and function usage.
• Added explicit type checks using stopifnot on function parameters.
• Replaced hard-coded variables with environment variables via .env.
• Migrated executing loops safely into exec/.
• Authored by alisadeghiaghili.

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PR created automatically by Jules for task 6593981717198510353 started by @alisadeghiaghili

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