fix: Accept any numeric tracking event value (#65)

`track` threw a `ClassCastException` for a tracking event value which
was not a `Double`.

- `TrackingEventDetails.getValue()` is an `Optional<Number>`, so `new
MutableTrackingEventDetails(99)` (an `Integer`) reached the provider and
failed the `(Double)` cast before any event was sent.
- The value is now converted with `Number.doubleValue()`, which is what
the LaunchDarkly `trackMetric` API takes.
- Added a test tracking an integer value.

<details>
<summary>Implementation details</summary>

The OpenFeature Java SDK does not constrain the numeric type an
application passes, and `MutableTrackingEventDetails` stores the
`Number` as given, so any of `Integer`, `Long`, `Float`, or `BigDecimal`
reached the cast. Only `Double` worked.

Testing: the change is covered by
`ProviderTest.itCanTrackAnIntegerTrackingEventValue`. The test suite
could not be run on this machine because Maven Central and the Gradle
plugin portal answered dependency resolution with HTTP 429 from this
network; CI runs the suite.
</details>


Link to Devin session:
https://app.devin.ai/sessions/fe1eb757fe694ef79f3d09f6307d4b47
Open in Devin Desktop:
https://app.devin.ai/desktop/session/fe1eb757fe694ef79f3d09f6307d4b47?variant=devin
Requested by: @kinyoklion

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Overview**
> Fixes **`track`** failing with a **`ClassCastException`** when
**`TrackingEventDetails`** carries a metric that is not a **`Double`**
(for example **`MutableTrackingEventDetails(99)`** with an
**`Integer`**).
> 
> The provider now reads **`Optional<Number>`** via
**`Number.doubleValue()`** before calling LaunchDarkly
**`trackMetric`**, matching the API’s double metric parameter. A unit
test asserts integer metrics are forwarded as **`99.0`**.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
d3177c0. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

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

@@ -266,7 +266,7 @@ public void track(String eventName, EvaluationContext ctx, TrackingEventDetails
         if (details != null) {
             Double metricValue = null;
             if (details.getValue().isPresent()) {
-                metricValue = (Double) details.getValue().get();
+                metricValue = details.getValue().get().doubleValue();
             }
             // Convert the Structure portion of the TrackingEventDetails into a key value
             // map.

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

@@ -214,4 +214,25 @@ public void itCanTrackFullTrackingEventDetails() {
                 valueConverter.toLdValue(new Value(trackingEventDetails)),
                 99.77);
     }
+
+    @Test
+    public void itCanTrackAnIntegerTrackingEventValue() {
+        EvaluationContext evaluationContext = new ImmutableContext("user-key");
+        EvaluationContextConverter evaluationContextConverter = new EvaluationContextConverter(null);
+        ValueConverter valueConverter = new ValueConverter(null);
+
+        TrackingEventDetails trackingEventDetails = new MutableTrackingEventDetails(99).add("currency", "USD");
+
+        OpenFeatureAPI.getInstance().setProvider(ldProvider);
+
+        OpenFeatureAPI
+                .getInstance()
+                .getClient().track("metric-key", evaluationContext, trackingEventDetails);
+
+        verify(mockedLdClient).trackMetric(
+                "metric-key",
+                evaluationContextConverter.toLdContext(evaluationContext),
+                valueConverter.toLdValue(new Value(trackingEventDetails)),
+                99.0);
+    }
 }