fix(deletions): Deletions hotfix

[0xKitsune]

This PR applies the hotfixes contained in 1.0.3 - 1.0.5, updating the following logic:

• Introduces pending_insertions_mutex to ensure that deletion and insertion updates are not interleaved into the pending_identities table.

• Updates process_identities task to process deletions immediately and process partial insertion batches when the next batch is deletion.