chore: Record FDv2 and test-data-source SDK capabilities (#201)

## Summary

Add `fdv2` and `testDataSource` to SDK metadata.

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Overview**
> Registers two **Rust Server SDK** capabilities in
`.sdk_metadata.json`: **`fdv2`** (introduced in **3.3**) and
**`testDataSource`** (introduced in **3.0**). This aligns published SDK
feature metadata with support already present in the SDK; no runtime or
API code changes.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
579dd14. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: beekld

.sdk_metadata.json

@@ -24,6 +24,9 @@
         "experimentation": {
           "introduced": "1.0"
         },
+        "fdv2": {
+          "introduced": "3.3"
+        },
         "inlineContextCustomEvents": {
           "introduced": "2.6"
         },
@@ -54,6 +57,9 @@
         "storingData": {
           "introduced": "1.0"
         },
+        "testDataSource": {
+          "introduced": "3.0"
+        },
         "track": {
           "introduced": "1.0"
         },