feat: add event enrichment client package

[ekjotmultani]

Summary

Event Enrichment client for analytics — the on-device companion that stamps device/app/session/identity context onto events and emits a Pinpoint-compatible JSON envelope, so events sent via the Kinesis/Firehose clients keep the analytics context Pinpoint used to provide automatically.

This PR contains core package implementation only (lib files, no example, no tests). The example app and unit tests are in stacked PRs based on this branch.

PR Stack (3-way split)

PR	Branch	Content
This PR (#7029)	feat/event-enrichment-client	Core package (lib only — 22 files)
#7076	feat/event-enrichment-client-example	Example app (92 files)
#7068	feat/event-enrichment-client-tests	Unit tests (5 files)

Structure

Dart/Flutter split, mirroring the Kinesis packages:

• amplify_event_enrichment_dart — pure-Dart core (client, EnrichedEvent, SessionManager, global fields, metadata, EventSink interface). No Flutter dependency.
• amplify_event_enrichment — Flutter wrapper: lifecycle observer, SharedPreferencesClientIdProvider, injectable DeviceMetadataProvider, re-exports the core.

Built on v3 Amplify Foundation (amplify_foundation_dart, Result<T>, sealed exceptions, AmplifyLogging).

Key decisions

• Shared device id: shared_preferences under com.amplifyframework.device_id, read-or-create — a cross-package contract shared with the Connect client (whichever inits first generates the UUID; the other reads it). Maps to native SharedPreferences/NSUserDefaults so a device gets one id everywhere.
• Zero default dependencies: device_info_plus is not a core dependency; device metadata comes from an injectable DeviceMetadataProvider defaulting to dart:io Platform. The EventSink ships as an interface only (no default sinks) — keeps enrichment transport-agnostic.

Verification

• Example app: see feat(amplify_event_enrichment): add example app #7076
• Tests: see test(amplify_event_enrichment): add unit tests #7068 (41 Dart + 6 Flutter, all passing)

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 43.23%. Comparing base (5d896ca) to head (b05a0ad).
⚠️ Report is 42 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7029      +/-   ##
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+ Coverage   43.22%   43.23%   +0.01%     
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  Files          99       99              
  Lines        7769     7769              
  Branches     3400     3401       +1     
==========================================
+ Hits         3358     3359       +1     
+ Misses       4411     4410       -1     

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[cadivus]

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