fix(rum): enable selective disabling of RUM per location (#34)

Fixes RUM configuration inheritance using std::optional

Previously, child locations couldn't disable RUM when parent enabled it
due to OR-based merge (`child || parent`).

**Enum values:**
- `Unset` = inherit from parent (default)
- `Disabled` = explicitly disabled (`DatadogRum Off`)
- `Enabled` = explicitly enabled (`DatadogRum On`)

**Example:**
```apache
DatadogRum On
<DatadogRumSettings>
  DatadogRumOption applicationId abc123
</DatadogRumSettings>

<Location /health>
  DatadogRum Off  # Now works correctly
</Location>
```

Author: pawelchcki

mod_datadog/src/rum/config.cpp

@@ -78,7 +78,7 @@ std::string make_rum_json_config(
 
 const char* enable_rum_ddog(cmd_parms* /* cmd */, void* cfg, int value) {
   auto* dir_conf = static_cast<Directory*>(cfg);
-  dir_conf->rum.enabled = (bool)value;
+  dir_conf->rum.enabled = static_cast<bool>(value);
   return NULL;
 }
 
@@ -178,7 +178,9 @@ namespace datadog::rum::conf {
 
 void merge_directory_configuration(Directory& out, const Directory& parent,
                                    const Directory& child) {
-  out.enabled = child.enabled || parent.enabled;
+  // If child explicitly set enabled, use child's value; otherwise inherit from
+  // parent
+  out.enabled = child.enabled.has_value() ? child.enabled : parent.enabled;
   out.snippet = child.snippet ? child.snippet : parent.snippet;
   out.app_id_tag =
       child.app_id_tag.empty() ? parent.app_id_tag : child.app_id_tag;

mod_datadog/src/rum/config.h

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <optional>
 #include <string>
 #include <unordered_map>
 
@@ -26,7 +27,7 @@ AP_INIT_TAKE_ARGV("DatadogRumOption", reinterpret_cast<cmd_func>(set_rum_option)
 namespace datadog::rum::conf {
 
 struct Directory final {
-  bool enabled = false;
+  std::optional<bool> enabled;  // nullopt = inherit from parent
   Snippet* snippet = nullptr;
   std::string version;
   std::unordered_map<std::string, std::string> config;

mod_datadog/src/rum/filter.cpp

@@ -96,7 +96,8 @@ int rum_output_filter(ap_filter_t* f, apr_bucket_brigade* bb) {
   auto* dir_conf = static_cast<Directory*>(
       ap_get_module_config(r->per_dir_config, &datadog_module));
 
-  if (!dir_conf->rum.enabled || dir_conf->rum.snippet == nullptr) {
+  // Only inject if explicitly enabled
+  if (dir_conf->rum.enabled != true || dir_conf->rum.snippet == nullptr) {
     return ap_pass_brigade(f->next, bb);
   }