Add requestBuilder() guidance to customizeRequest() Javadoc body

Author: gyeo009

mcp-core/src/main/java/io/modelcontextprotocol/client/transport/HttpClientSseClientTransport.java

@@ -245,7 +245,9 @@ public Builder requestBuilder(HttpRequest.Builder requestBuilder) {
 		 * at build time</b>. Any headers set here (e.g., {@code Authorization}) are
 		 * frozen into the template and copied to every subsequent request via
 		 * {@code requestBuilder.copy()}. They <b>cannot be updated</b> after the
-		 * transport is built.
+		 * transport is built. For stable headers, consider using
+		 * {@link #requestBuilder(HttpRequest.Builder)} to pre-configure the shared
+		 * request template directly.
 		 * <p>
 		 * For dynamic, per-request customization (e.g., OAuth token refresh), use
 		 * {@link #httpRequestCustomizer(McpSyncHttpClientRequestCustomizer)} or

mcp-core/src/main/java/io/modelcontextprotocol/client/transport/HttpClientStreamableHttpTransport.java

@@ -711,7 +711,9 @@ public Builder requestBuilder(HttpRequest.Builder requestBuilder) {
 		 * at build time</b>. Any headers set here (e.g., {@code Authorization}) are
 		 * frozen into the template and copied to every subsequent request via
 		 * {@code requestBuilder.copy()}. They <b>cannot be updated</b> after the
-		 * transport is built.
+		 * transport is built. For stable headers, consider using
+		 * {@link #requestBuilder(HttpRequest.Builder)} to pre-configure the shared
+		 * request template directly.
 		 * <p>
 		 * For dynamic, per-request customization (e.g., OAuth token refresh), use
 		 * {@link #httpRequestCustomizer(McpSyncHttpClientRequestCustomizer)} or