feat(msdk-4325): add tcf 2.4 features standard text to TCFData

[asadraza-usercentrics]

Description:

Summary

IAB TCF v2.4 / IAB Policies v5.0.b introduces a new mandatory standard
text for the "Features" category, sourced from the GVL's new
standardTexts.features field. The native mobile-sdk core already
exposes this as featuresStandardText on TCFData (see the companion
mobile-sdk PR) and renders it in the SDK's own prebuilt UI — this PR
adds the same field to the Flutter plugin's TCFData model so apps
calling getTCFData() directly see it too.

Changes

• lib/src/model/tcf_data.dart: add featuresStandardText (nullable String) to the TCFData class
• lib/src/internal/serializer/tcf_data_serializer.dart: deserialize the new field from the native method-channel payload
• android/.../TCFDataSerializer.kt + ios/.../TCFDataSerializer.swift: native→Dart bridge serializers updated to include the field
• android/.../GetTCFDataMock.kt + test/.../get_tcf_data_bridge_test.mock.dart: test fixtures updated to cover the new field

Testing

• flutter test — all 67 tests passing, including the updated getTCFData bridge test
• Verified end-to-end against a local build of the native SDK (same ticket): ran the example app on Android and iOS, confirmed featuresStandardText is populated from a live GVL response and renders correctly in the second-layer Features section

Notes for reviewers

• Pure additive change — the field is optional/nullable on both the Dart and native sides, so existing consumers are unaffected.
• Depends on the native SDK field existing (mobile-sdk MSDK-4325/4216 PR) to return a non-null value at runtime.