Add flutter_aepoptimize plugin for Adobe Optimize SDK

[akhiljain1907]

Introduces a complete Flutter method-channel plugin wrapping the native AEP Optimize iOS (AEPOptimize ~>5.0) and Android (optimize via BOM 3.x) SDKs. Multiple native API overloads (no-callback, callback, callback+timeout) are consolidated into single Dart methods with optional parameters.

Dart API: Optimize.updatePropositions, getPropositions, onPropositionsUpdate,
clearCachedPropositions. Models: DecisionScope, OptimizeProposition, Offer,
OfferType. Offer tracking: displayed(), tapped(), generateDisplayInteractionXdm(),
generateTapInteractionXdm(). Proposition: generateReferenceXdm().

Includes 636 lines of Dart unit tests covering API invocation, response decoding, model roundtrips, enum conversions, listener callbacks, and edge cases.

Description

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Motivation and Context

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Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.