fix: Include an error code in provider error events (#68)

**Requirements**

- [x] I have added test coverage for new or changed functionality
- [x] I have followed the repository's [pull request submission
guidelines](../blob/main/CONTRIBUTING.md#submitting-pull-requests)
- [ ] I have validated my changes against all supported platform
versions

**Related issues**

OFP requirement 5.1.5 (sdk-specs `OFP-openfeature-provider-behavior`):
`PROVIDER_ERROR` events SHOULD populate the event details' error code.

**Describe the solution you've provided**

When the LaunchDarkly data source transitions to `OFF`, the emitted
`PROVIDER_ERROR` event details now include `ErrorCode.GENERAL` alongside
the existing message:

```java
emitProviderError(ProviderEventDetails.builder().message(message).errorCode(ErrorCode.GENERAL).build());
```

Added `LifeCycleTest.itIncludesAnErrorCodeInErrorEvents`.

**Describe alternatives you've considered**

A more specific code (e.g. `PROVIDER_FATAL` for 401/403) was not used;
OFP does not define a mapping, and the Python provider already uses
`GENERAL` for the same transition. Choosing per-error codes would be a
cross-SDK decision.

**Additional context**

OpenFeature Java SDK 1.23.0 fixed propagation of `errorCode` from
provider event details to handler `EventDetails`, so handlers now
observe this value.

Link to Devin session:
https://app.devin.ai/sessions/929f5530882d40bc95e55391e97536d5
Open in Devin Desktop:
https://app.devin.ai/desktop/session/929f5530882d40bc95e55391e97536d5?variant=devin
Requested by: @kinyoklion

[SDK-3254](https://launchdarkly.atlassian.net/browse/SDK-3254)


[SDK-3254]:
https://launchdarkly.atlassian.net/browse/SDK-3254?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Overview**
> Aligns **PROVIDER_ERROR** event details with OpenFeature provider
behavior (OFP 5.1.5) by setting **`ErrorCode.GENERAL`** when the
LaunchDarkly data source enters **`OFF`** and the provider moves to
error state. Error messages are unchanged; handlers can now read
**`detail.getErrorCode()`** (supported after OpenFeature Java SDK
1.23.0).
> 
> Adds **`LifeCycleTest.itIncludesAnErrorCodeInErrorEvents`** to assert
the error code on **`PROVIDER_ERROR`** using the existing delayed
failing data source setup.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
dd3f67a. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Author: kinyoklion

src/main/java/com/launchdarkly/openfeature/serverprovider/Provider.java

@@ -227,7 +227,7 @@ private void handleDataSourceStatus(DataSourceStatusProvider.Status res, Complet
                 var message = res.getLastError() != null
                     ? res.getLastError().toString()
                     : "the provider has encountered a permanent error or has been shutdown";
-                emitProviderError(ProviderEventDetails.builder().message(message).build());
+                emitProviderError(ProviderEventDetails.builder().message(message).errorCode(ErrorCode.GENERAL).build());
             }
         }
     }

src/test/java/com/launchdarkly/openfeature/serverprovider/LifeCycleTest.java

@@ -7,6 +7,7 @@
 import com.launchdarkly.sdk.server.subsystems.ComponentConfigurer;
 import com.launchdarkly.sdk.server.subsystems.DataSource;
 import com.launchdarkly.sdk.server.subsystems.DataSourceUpdateSink;
+import dev.openfeature.sdk.ErrorCode;
 import dev.openfeature.sdk.ImmutableContext;
 import dev.openfeature.sdk.OpenFeatureAPI;
 import dev.openfeature.sdk.ProviderEvent;
@@ -357,6 +358,25 @@ public void itIncludesTheDataSourceErrorInErrorEvents() throws Exception {
         assertTrue(message.contains("bad"));
     }
 
+    @Test
+    public void itIncludesAnErrorCodeInErrorEvents() throws Exception {
+        var config = new LDConfig.Builder()
+            .startWait(Duration.ZERO)
+            .dataSource(new DelayedDataSourceFactory(Duration.ofMillis(100), false, true))
+            .events(Components.noEvents())
+            .build();
+        var provider = new Provider("fake-key", config);
+        CompletableFuture<ErrorCode> errorCode = new CompletableFuture<>();
+
+        OpenFeatureAPI.getInstance().on(ProviderEvent.PROVIDER_ERROR, (detail) -> {
+            errorCode.complete(detail.getErrorCode());
+        });
+
+        OpenFeatureAPI.getInstance().setProviderAndWait(provider);
+
+        assertEquals(ErrorCode.GENERAL, errorCode.get(1000, TimeUnit.MILLISECONDS));
+    }
+
     @Test
     public void itIncludesHttpDataSourceErrorInErrorEvents() throws Exception {
         var config = new LDConfig.Builder()