[WIP] Rewrite email ingestion driver for non-interactive use

[Copilot]

Thanks for assigning this issue to me. I'm starting to work on it and will keep this PR's description up to date as I form a plan and make progress.

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This section details on the original issue you should resolve

<issue_title>Rewrite email ingestion driver</issue_title>
<issue_description>Currently to ingest email (*.eml) data you run python tools/test_email.py . and enter the command @add_messages --path "gmail/email_dump".

I'd rather have a non-interactive tool similar to tools/ingest_vtt.py (e.g. tools/ingest_email.py) with a similar command line. It should have all the features of @add_messages, e.g. skipping alread-indexed messages, recovering from failures (by continuing with the next message), displaying detailed progress.

Possibly we could let it do batching like ingest_vtt, just with a default batch size of 1 (to match @add_messages).

The directory(ies) or file(s) to index should be simple command line args (not flags).</issue_description>

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Comments on the Issue (you are @copilot in this section)

• Fixes Rewrite email ingestion driver #76

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