Add bulk test coverage for Account trigger validations

[sonalguptaabd-bit]

Summary

Some existing Account trigger validations do not have explicit tests
for bulk insert scenarios. Without these tests, it is hard to confirm
that validations behave correctly when multiple Account records are
processed together.

Suggested Solution

Add additional test methods in test classes to verify that existing
Account validations:

• Work correctly for bulk insert operations
• Handle mixed valid and invalid records without throwing
  unexpected errors

This change will be strictly test-only and will not modify any
production logic.

Alternative Solutions

No alternative solutions proposed. Existing validation logic is
correct; only additional tests are needed to cover bulk scenarios.

Code of Conduct

• I agree to follow this project's Code of Conduct

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