fix(sentinel): address SpotBugs violations in SentinelConfig

Fixed three SpotBugs issues:

1. EI2 (Expose Internal Representation - Builder):
   - Added @Singular annotation to sentinelHosts field
   - Lombok now creates defensive copies in builder methods

2. EI (Expose Internal Representation - Getter):
   - Replaced @Getter with custom getSentinelHosts() method
   - Returns Collections.unmodifiableList() to prevent external modification

3. CT (Constructor Throws Exception):
   - Made HostPort class final to prevent finalizer attacks
   - Constructor validation now safe from subclass finalizer exploits

All 350 tests pass, SpotBugs verification successful.

Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: bsbodden

core/src/main/java/com/redis/vl/redis/SentinelConfig.java

@@ -1,9 +1,11 @@
 package com.redis.vl.redis;
 
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 import lombok.Builder;
 import lombok.Getter;
+import lombok.Singular;
 
 /**
  * Configuration for Redis Sentinel connections.
@@ -13,30 +15,38 @@
  *
  * <p>Python reference: redisvl/redis/connection.py - _parse_sentinel_url
  */
-@Getter
 @Builder
 public class SentinelConfig {
 
   /** List of Sentinel host:port pairs */
-  private final List<HostPort> sentinelHosts;
+  @Singular private final List<HostPort> sentinelHosts;
 
   /** Sentinel service/master name (default: "mymaster") */
-  @Builder.Default private final String serviceName = "mymaster";
+  @Getter @Builder.Default private final String serviceName = "mymaster";
 
   /** Redis database number (optional) */
-  private final Integer database;
+  @Getter private final Integer database;
 
   /** Username for authentication (optional) */
-  private final String username;
+  @Getter private final String username;
 
   /** Password for authentication (optional) */
-  private final String password;
+  @Getter private final String password;
 
   /** Connection timeout in milliseconds */
-  @Builder.Default private final int connectionTimeout = 2000;
+  @Getter @Builder.Default private final int connectionTimeout = 2000;
 
   /** Socket timeout in milliseconds */
-  @Builder.Default private final int socketTimeout = 2000;
+  @Getter @Builder.Default private final int socketTimeout = 2000;
+
+  /**
+   * Get an unmodifiable view of the Sentinel hosts list.
+   *
+   * @return Unmodifiable list of Sentinel host:port pairs
+   */
+  public List<HostPort> getSentinelHosts() {
+    return Collections.unmodifiableList(sentinelHosts);
+  }
 
   /**
    * Parse a Sentinel URL into a SentinelConfig.
@@ -216,7 +226,7 @@ private static HostPort parseHostPort(String hostPort) {
 
   /** Represents a host:port pair for Sentinel nodes */
   @Getter
-  public static class HostPort {
+  public static final class HostPort {
     private final String host;
     private final int port;