fix: prevent object expansion in placeholders after SET clause

[wellwelwel]

Fixes object expansion in placeholders positioned after the SET clause (e.g. WHERE, subqueries) by resetting setIndex after the first object is expanded, so only the SET ? placeholder uses objectToValues.

---

❌ Before:

format('UPDATE users SET ? WHERE id = ?', [{ name: 'foo' }, { id: 1 }])

UPDATE users SET `name` = 'foo' WHERE id = `id` = 1
--                                         ^^^^^^^^^ 
--                                         expands to key=value (vulnerable)

✅ After:

format('UPDATE users SET ? WHERE id = ?', [{ name: 'foo' }, { id: 1 }])

UPDATE users SET `name` = 'foo' WHERE id = '[object Object]'
--                                         ^^^^^^^^^^^^^^^^^
--                                         safely stringified

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (968d07e) to head (6174853).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main        #5   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines          361       362    +1     
=========================================
+ Hits           361       362    +1     

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