## Description
This PR optimizes message queries by explicitly filtering with
`account_id` so the database can use the existing indexes more
efficiently.
Changes:
- Add `account_id` to message query filters to improve index
utilization.
- Update `last_incoming_message` query to include `account_id`.
- Avoid unnecessary preloading of `contact_inboxes` where it is not
required.
- Update specs to ensure `account_id` is set correctly in
message-related tests.
These changes reduce query cost and improve performance for message
lookups, especially on large accounts.
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Co-authored-by: Pranav <pranav@chatwoot.com>
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