fix: clarify gap-detection comment in bindKeywordArguments

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Co-authored-by: casperlamboo <6638028+casperlamboo@users.noreply.github.com>

Author: Copilot

src/ast/fn_application_expr.cpp

@@ -64,8 +64,9 @@ std::optional<std::vector<eval::Value>> bindKeywordArguments(
         bound.push_back(slot.value());
     }
 
-    // If any slot beyond the bound range has a value there is a gap (a required
-    // earlier argument is missing while a later one was supplied via keyword).
+    // If any slot beyond the consecutively-filled slots from the start has a
+    // value there is a gap (a required earlier argument is missing while a
+    // later one was supplied via keyword).
     // Return nullopt so the caller can report InvalidNumberOfArguments.
     for (size_t i = bound.size(); i < slots.size(); ++i)
     {