More robust clean up after unexpected docgen process exits.

[hsubox76]

• Put cleanup for both docs and toc generation into a cleanup function that's run on process exit and SIGINT (ctrl-C) to ensure auth files especially are returned to their original state no matter what.
• Clean top level temp/ json dir before every run.

The cleanup process used to run in a "finally" block which is fine for catching errors caused by the specific code but doesn't account for a SIGINT or some other unexpected interruption.

I think I put enough checks in the cleanup code to make sure the steps don't error but I also wrapped it in a try/catch just in case with a warning to watch out for changed files.

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Latest commit: 9b7d998

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[google-oss-bot]

Size Report ¹

Affected Products

No changes between base commit (3883133) and merge commit (fcdac42).

Test Logs

• Base (3883133): https://github.com/firebase/firebase-js-sdk/actions/runs/9181396307
• Merge (fcdac42): https://github.com/firebase/firebase-js-sdk/actions/runs/9197072185

1. https://storage.googleapis.com/firebase-sdk-metric-reports/hA8yq9a9Br.html

[google-oss-bot]

Size Analysis Report ¹

Affected Products

No changes between base commit (3883133) and merge commit (fcdac42).

Test Logs

• Base (3883133): https://github.com/firebase/firebase-js-sdk/actions/runs/9181396307
• Merge (fcdac42): https://github.com/firebase/firebase-js-sdk/actions/runs/9197072185

1. https://storage.googleapis.com/firebase-sdk-metric-reports/PbW2iar352.html