scripts: de-duplicate and harden the close_pull_requests_with_*.sh backlog jobs

[cclauss]

This is a replica of @priya-sundaram-dev pull request:

• scripts: de-duplicate and harden the close_pull_requests_with_*.sh backlog jobs #15169

This is a follow-up to:

• priya-sundaram-dev as a maintainer? #15081

Extract the five byte-for-byte-identical backlog-closing scripts into one parameterized close_pull_requests_with_label.sh and make each named script a thin wrapper. Addresses the recommendations from #15168:

• Correctness: filter by label server-side (gh pr list --label) instead of listing all ~900 open PRs and matching client-side, so no PR is skipped by an arbitrary --limit cap.
• De-duplication: one implementation removes the drift between copies (some had sleep 2, one had it commented out, two had none).
• Throttling: a single, deliberate SLEEP (default 2s) between closes.
• Safety rails: set -euo pipefail, explicit --repo, and a DRY_RUN=1 preview mode that prints what would close before a maintainer commits.
• Machine-readable summary (CLOSED_COUNT/CLOSED_PRS) so the Hacktoberfest tracker can be updated from script output.

Describe your change:

• Fix scripts
• Fix a bug or typo in an existing algorithm?
• Add or change doctests? -- Note: Please avoid changing both code and tests in a single pull request.
• Documentation change?

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is the work of @priya-sundaram-dev
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new Python files are placed inside an existing directory.
• All filenames are in all lowercase characters with no spaces or dashes.
• All functions and variable names follow Python naming conventions.
• All function parameters and return values are annotated with Python type hints.
• All functions have doctests that pass the automated testing.
• All new algorithms include at least one URL that points to Wikipedia or another similar explanation.
• If this pull request resolves one or more open issues, then the description above includes the issue number(s) with a closing keyword: "Fixes #ISSUE-NUMBER".

[cclauss]

@priya-sundaram-dev With these changes, I ran scripts/close_pull_requests_with_require_tests.sh, which output:
CLOSED_COUNT=24 CLOSED_PRS=14973,14732,14582,14478,14352,14342,14314,14303,14086,14045,14027,14019,14004,13883,13823,13822,13781,13774,13761,13742,13712,13655,13600,13523

Please create a PR to update docs/hacktober_2026_prep.md