Add immediate_hydration configuration to ReactOnRailsPro

Move immediate_hydration from ReactOnRails to ReactOnRailsPro
configuration since it's a Pro-only feature.

Changes:
- Add DEFAULT_IMMEDIATE_HYDRATION constant (default: false)
- Add immediate_hydration to attr_accessor list
- Add immediate_hydration parameter to initialize method
- Add immediate_hydration assignment in initialize
- Add immediate_hydration to configuration instantiation

This prepares for removing immediate_hydration from the core
ReactOnRails configuration in the next commit.

Author: claude

react_on_rails_pro/lib/react_on_rails_pro/configuration.rb

@@ -32,7 +32,8 @@ def self.configuration
       rsc_payload_generation_url_path: Configuration::DEFAULT_RSC_PAYLOAD_GENERATION_URL_PATH,
       rsc_bundle_js_file: Configuration::DEFAULT_RSC_BUNDLE_JS_FILE,
       react_client_manifest_file: Configuration::DEFAULT_REACT_CLIENT_MANIFEST_FILE,
-      react_server_client_manifest_file: Configuration::DEFAULT_REACT_SERVER_CLIENT_MANIFEST_FILE
+      react_server_client_manifest_file: Configuration::DEFAULT_REACT_SERVER_CLIENT_MANIFEST_FILE,
+      immediate_hydration: Configuration::DEFAULT_IMMEDIATE_HYDRATION
     )
   end
 
@@ -59,6 +60,7 @@ class Configuration # rubocop:disable Metrics/ClassLength
     DEFAULT_RSC_BUNDLE_JS_FILE = "rsc-bundle.js"
     DEFAULT_REACT_CLIENT_MANIFEST_FILE = "react-client-manifest.json"
     DEFAULT_REACT_SERVER_CLIENT_MANIFEST_FILE = "react-server-client-manifest.json"
+    DEFAULT_IMMEDIATE_HYDRATION = false
 
     attr_accessor :renderer_url, :renderer_password, :tracing,
                   :server_renderer, :renderer_use_fallback_exec_js, :prerender_caching,
@@ -68,7 +70,7 @@ class Configuration # rubocop:disable Metrics/ClassLength
                   :renderer_request_retry_limit, :throw_js_errors, :ssr_timeout,
                   :profile_server_rendering_js_code, :raise_non_shell_server_rendering_errors, :enable_rsc_support,
                   :rsc_payload_generation_url_path, :rsc_bundle_js_file, :react_client_manifest_file,
-                  :react_server_client_manifest_file
+                  :react_server_client_manifest_file, :immediate_hydration
 
     def initialize(renderer_url: nil, renderer_password: nil, server_renderer: nil, # rubocop:disable Metrics/AbcSize
                    renderer_use_fallback_exec_js: nil, prerender_caching: nil,
@@ -79,7 +81,8 @@ def initialize(renderer_url: nil, renderer_password: nil, server_renderer: nil,
                    renderer_request_retry_limit: nil, throw_js_errors: nil, ssr_timeout: nil,
                    profile_server_rendering_js_code: nil, raise_non_shell_server_rendering_errors: nil,
                    enable_rsc_support: nil, rsc_payload_generation_url_path: nil,
-                   rsc_bundle_js_file: nil, react_client_manifest_file: nil, react_server_client_manifest_file: nil)
+                   rsc_bundle_js_file: nil, react_client_manifest_file: nil, react_server_client_manifest_file: nil,
+                   immediate_hydration: nil)
       self.renderer_url = renderer_url
       self.renderer_password = renderer_password
       self.server_renderer = server_renderer
@@ -105,6 +108,7 @@ def initialize(renderer_url: nil, renderer_password: nil, server_renderer: nil,
       self.rsc_bundle_js_file = rsc_bundle_js_file
       self.react_client_manifest_file = react_client_manifest_file
       self.react_server_client_manifest_file = react_server_client_manifest_file
+      self.immediate_hydration = immediate_hydration
     end
 
     def setup_config_values