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/protocol/STAmount.cpp

@@ -1612,7 +1612,7 @@ mulRoundImpl(STAmount const& v1, STAmount const& v2, Asset const& asset, bool ro
     STAmount result = [&]() {
         // If appropriate, tell Number to round down.  This gives the desired
         // result from STAmount::canonicalize.
-        MightSaveRound const savedRound(Number::towards_zero);
+        MightSaveRound const savedRound(Number::rounding_mode::towards_zero);
         return STAmount(asset, amount, offset, resultNegative);
     }();