Preserve client overrides in Luna comparison

Summary:
Pass explicit client-owned option names to `McrouterOptionsBase::compare()` so Luna comparison skips only `config_params` and `router_name` overrides while preserving missing-key validation for every Luna-managed option. Apply both overrides as typed fields after Luna materialization, avoiding delimiter-based serialization.

Review context

This child responds to the following comment from Anton (`alikhtarov`) on D113813215:

> Can we reorder the logic here to avoid hasConfigParamsOverride? I.e.
>
> 1) construct lunaOptions (copy config_params from before)
> 2) apply luna settings
> 3) compare lunaOptions with currentOptions (need to rewrite the comparison function)
>
> This is probably more correct as well as we're comparing actual options struct instead of serialized representations.

What this addresses:

- Removes the `hasConfigParamsOverride` flag and post-comparison `remove_if`; client-owned options are represented explicitly.
- Keeps overridden `config_params` and `router_name` out of raw Luna comparison and overlays them as typed fields after Luna application.
- Retains existing missing-key errors for every non-overridden Luna-managed option.

What this does not address:

- It does not reorder the entire pipeline to apply Luna before comparison.
- It does not compare two `McrouterOptions` structs; non-overridden options still use the existing raw Luna-map comparison.

This narrower scope avoids introducing generic typed-comparison infrastructure and changing scalar normalization semantics while addressing the override-handling concern that motivated the comment.

Reviewed By: alikhtarov

Differential Revision: D114116126

fbshipit-source-id: 1e0ed10bfe3fa990fb8881e2a44e6c7d2d7b4f9b

Author: Vrishal Kulkarni

mcrouter/options.cpp

@@ -270,12 +270,16 @@ vector<McrouterOptionError> McrouterOptionsBase::updateFromDict(
 }
 
 vector<McrouterOptionMismatch> McrouterOptionsBase::compare(
-    const std::unordered_map<std::string, std::string>& new_opts) const {
+    const std::unordered_map<std::string, std::string>& new_opts,
+    const std::unordered_set<std::string>& ignored_opts) const {
   vector<McrouterOptionMismatch> errors;
-  forEach([&errors, &new_opts](
+  forEach([&errors, &new_opts, &ignored_opts](
               const string& name,
               McrouterOptionData::Type type,
               const boost::any& value) {
+    if (ignored_opts.contains(name)) {
+      return;
+    }
     auto it = new_opts.find(name);
     if (it == new_opts.end()) {
       McrouterOptionMismatch e;

mcrouter/options.h

@@ -10,6 +10,7 @@
 #include <functional>
 #include <string>
 #include <unordered_map>
+#include <unordered_set>
 #include <vector>
 
 #include <boost/any.hpp>
@@ -84,7 +85,8 @@ class McrouterOptionsBase {
       const std::unordered_map<std::string, std::string>& new_opts);
 
   virtual std::vector<McrouterOptionMismatch> compare(
-      const std::unordered_map<std::string, std::string>& new_opts) const;
+      const std::unordered_map<std::string, std::string>& new_opts,
+      const std::unordered_set<std::string>& ignored_opts = {}) const;
 
   virtual ~McrouterOptionsBase() {}