fix #7847: optimize DeleteGuestCustomersAsync using batch deletes

[Parthiban6316]

Problem

The current DeleteGuestCustomersAsync method deletes all guest
customers in a single massive DB operation using temporary tables
(tmp_guestsToDelete, tmp_guestsAddressesToDelete). On large stores
this causes:

• SQL timeout errors / long running DB locks
• Store main thread blocked waiting on DB
• Failed tasks leaving orphan tmp_ tables behind
• Next run crashing with "Table tmp_guestsToDelete already exists"

Solution

Replaced single bulk delete with batched processing (500 records
per batch). Each batch:

• Fetches a small set of guest IDs
• Deletes their generic attributes
• Deletes their addresses
• Deletes the customers themselves

Benefits

• No more temp tables — no orphan table risk
• Short DB locks per batch instead of one giant lock
• Survives large datasets without timeouts
• Faster overall due to smaller focused queries

Fixes #7847