Add index for mysql and postgres

[sdil]

Motivation / Background

I'm trying to optimize table schema by addind index on both MySQL and Postgres adapter.

Details

I noticed that the SELECT query access pattern for the queue tables always has the WHERE acked = false and ORDER BY "offset" ASC clauses. For PostgreSQL, I added a partial index to optimize this query, and for MySQL, I added an index on this column.

Disclaimer: Claude Code helped me with this optimization.

Alternative approaches considered (if applicable)

N/A

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