fix: revert all unrelated upstream develop changes from phase-7 PR

Reverts 259 files that carried unrelated upstream changes through the
phase-6 merge: enum class removals (cppcoreguidelines-use-enum-class),
scoped_lock→lock_guard conversions (modernize-use-scoped-lock),
nodestore Backend API changes (void const* key), .clang-tidy config,
test infrastructure deletions, and miscellaneous develop changes.

These changes belong on develop, not in the telemetry PR chain.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/libxrpl/ledger/CachedView.cpp

@@ -30,7 +30,7 @@ CachedViewImpl::read(Keylet const& k) const
 
     auto const digest = [&]() -> std::optional<uint256> {
         {
-            std::lock_guard const lock(mutex_);
+            std::scoped_lock const lock(mutex_);
             auto const iter = map_.find(k.key);
             if (iter != map_.end())
             {
@@ -66,7 +66,7 @@ CachedViewImpl::read(Keylet const& k) const
         // Avoid acquiring this lock unless necessary. It is only necessary if
         // the key was not found in the map_. The lock is needed to add the key
         // and digest.
-        std::lock_guard const lock(mutex_);
+        std::scoped_lock const lock(mutex_);
         map_.emplace(k.key, *digest);
     }
     if (!sle || !k.check(*sle))