fix: NotEqualTo trigger no longer matches non-existent properties

[nan-li]

Description

One Line Summary

In-app "not_equal" trigger no longer matches non-existent properties.

Details

Motivation

• Changes the behavior of trigger evaluation when a property doesn't exist.
• Previously, a trigger with NotEqualTo operator would return true for non-existent properties (e.g., subscription_type != "premium" would match users without any subscription_type set).
• Now, only the NotExists operator returns true for non-existent properties. NotEqualTo requires the property to exist with a different value.
• This provides stricter trigger matching where NotEqualTo only matches users who have explicitly set a value that differs from the trigger value.

Motivation

• Consistency in in-app, otherwise these IAMs should display immediately on app open.
• Previously only the first display would show but subsequent ones would not due to this logic that blocks if an IAM has been seen already

Testing

Unit testing

Manual testing

iPhone 18.5 simulator

Affected code checklist

• Notifications
  • Display
  • Open
  • Push Processing
  • Confirm Deliveries
• Outcomes
• Sessions
• In-App Messaging
• REST API requests
• Public API changes

Checklist

Overview

• I have filled out all REQUIRED sections above
• PR does one thing
  • If it is hard to explain how any codes changes are related to each other then it most likely needs to be more than one PR
• Any Public API changes are explained in the PR details and conform to existing APIs

Testing

• I have included test coverage for these changes, or explained why they are not needed
• All automated tests pass, or I explained why that is not possible
• I have personally tested this on my device, or explained why that is not possible

Final pass

• Code is as readable as possible.
  • Simplify with less code, followed by splitting up code into well named functions and variables, followed by adding comments to the code.
• I have reviewed this PR myself, ensuring it meets each checklist item
  • WIP (Work In Progress) is ok, but explain what is still in progress and what you would like feedback on. Start the PR title with "WIP" to indicate this.

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This change is 

[abdulraqeeb33]

this looks good to me @nan-li . Can we write some tests for this?