feat: Update launchdarkly_event_source_client to version 2.2.0 (#302)

<!-- CURSOR_SUMMARY -->
> [!NOTE]
> **Low Risk**
> Single dependency pin change with no logic edits; behavior depends on
what shipped in event_source_client 2.2.0 elsewhere in the monorepo.
> 
> **Overview**
> Bumps the pinned **`launchdarkly_event_source_client`** dependency in
`launchdarkly_common_client` from **2.1.0** to **2.2.0**, so the shared
client layer uses the latest in-repo SSE package for streaming flag
updates.
> 
> There are **no application code changes** in this PR—only the
`pubspec.yaml` version pin.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
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code reviews on this repo. Configure
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<!-- /CURSOR_SUMMARY -->

Author: kinyoklion

packages/common_client/pubspec.yaml

@@ -10,7 +10,7 @@ environment:
 dependencies:
   http: ^1.1.2
   launchdarkly_dart_common: 1.8.1
-  launchdarkly_event_source_client: 2.1.0
+  launchdarkly_event_source_client: 2.2.0
   crypto: ^3.0.3
   uuid: ">= 3.0.7 <5.0.0"