Add Prometheus metrics integration and refactor API error handling

Introduces Prometheus metrics support with a new MetricsRecorder and documentation (METRICS.md). Refactors OllamaAPI methods to improve error handling, reduce checked exceptions, and record metrics for API calls. Updates dependencies in pom.xml to include Prometheus and Guava. Adds MetricsRecorder class and updates tests for metrics integration.

pom.xml

@@ -306,6 +306,19 @@
             <version>1.21.3</version>
             <scope>test</scope>
         </dependency>
+
+        <!-- Prometheus metrics dependencies -->
+        <dependency>
+            <groupId>io.prometheus</groupId>
+            <artifactId>simpleclient</artifactId>
+            <version>0.16.0</version>
+        </dependency>
+
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+            <version>33.5.0-jre</version>
+        </dependency>
     </dependencies>
 
     <distributionManagement>