fix(telemetry): satisfy clang-tidy const-correctness and redundant-parens

CI enabled more clang-tidy checks via the upstream merge:
- DiscardScope discardScope -> const (misc-const-correctness)
- drop the (::max)() Windows macro-guard parens; NOMINMAX is defined
  project-wide so the bare form is correct (readability-redundant-parentheses)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/libxrpl/telemetry/SpanGuard.cpp

@@ -361,7 +361,7 @@ SpanGuard::discard()
             // flag leak-proof if a later phase can hand back a non-recording
             // span (e.g. honoring a non-sampled remote parent during
             // propagation), so it can never spill onto the next span.
-            DiscardScope discardScope;
+            DiscardScope const discardScope;
             impl_->span->End();
         }
         impl_->span = nullptr;  // prevent ~Impl from calling End() again

src/libxrpl/telemetry/Telemetry.cpp

@@ -131,14 +131,13 @@ public:
 
     bool
     ForceFlush(
-        std::chrono::microseconds timeout = (std::chrono::microseconds::max)()) noexcept override
+        std::chrono::microseconds timeout = std::chrono::microseconds::max()) noexcept override
     {
         return delegate_->ForceFlush(timeout);
     }
 
     bool
-    Shutdown(
-        std::chrono::microseconds timeout = (std::chrono::microseconds::max)()) noexcept override
+    Shutdown(std::chrono::microseconds timeout = std::chrono::microseconds::max()) noexcept override
     {
         return delegate_->Shutdown(timeout);
     }