Eliminate spdlog dependency (#773)

Removes the vendored spdlog library (~12,000 lines) and replaces it with a purpose-built logging system in zencore (~1,800 lines). The new implementation provides the same functionality with fewer abstractions, no shared_ptr overhead, and full control over the logging pipeline.

### What changed

**New logging core in zencore/logging/:**
- LogMessage, Formatter, Sink, Logger, Registry - core abstractions matching spdlog's model but simplified
- AnsiColorStdoutSink - ANSI color console output (replaces spdlog stdout_color_sink)
- MsvcSink - OutputDebugString on Windows (replaces spdlog msvc_sink)
- AsyncSink - async logging via BlockingQueue worker thread (replaces spdlog async_logger)
- NullSink, MessageOnlyFormatter - utility types
- Thread-safe timestamp caching in formatters using RwLock

**Moved to zenutil/logging/:**
- FullFormatter - full log formatting with timestamp, logger name, level, source location, multiline alignment
- JsonFormatter - structured JSON log output
- RotatingFileSink - rotating file sink with atomic size tracking

**API changes:**
- Log levels are now an enum (LogLevel) instead of int, eliminating the zen::logging::level namespace
- LoggerRef no longer wraps shared_ptr - it holds a raw pointer with the registry owning lifetime
- Logger error handler is wired through Registry and propagated to all loggers on registration
- Logger::Log() now populates ThreadId on every message

**Cleanup:**
- Deleted thirdparty/spdlog/ entirely (110+ files)
- Deleted full_test_formatter (was ~80% duplicate of FullFormatter)
- Renamed snake_case classes to PascalCase (full_formatter -> FullFormatter, json_formatter -> JsonFormatter, sentry_sink -> SentrySink)
- Removed spdlog from xmake dependency graph

### Build / test impact

- zencore no longer depends on spdlog
- zenutil and zenvfs xmake.lua updated to drop spdlog dep
- zentelemetry xmake.lua updated to drop spdlog dep
- All existing tests pass, no test changes required beyond formatter class renames

1 files changed, 7 insertions, 7 deletions

diff --git a/src/zenremotestore/operationlogoutput.cpp b/src/zenremotestore/operationlogoutput.cpp
index 7ed93c947..5ed844c9d 100644
--- a/src/zenremotestore/operationlogoutput.cpp
+++ b/src/zenremotestore/operationlogoutput.cpp
@@ -3,6 +3,7 @@
 #include <zenremotestore/operationlogoutput.h>
 
 #include <zencore/logging.h>
+#include <zencore/logging/logger.h>
 
 ZEN_THIRD_PARTY_INCLUDES_START
 #include <gsl/gsl-lite.hpp>
@@ -30,13 +31,11 @@ class StandardLogOutput : public OperationLogOutput
 {
 public:
 	StandardLogOutput(LoggerRef& Log) : m_Log(Log) {}
-	virtual void EmitLogMessage(int LogLevel, std::string_view Format, fmt::format_args Args) override
+	virtual void EmitLogMessage(const logging::LogPoint& Point, fmt::format_args Args) override
 	{
-		if (m_Log.ShouldLog(LogLevel))
+		if (m_Log.ShouldLog(Point.Level))
 		{
-			fmt::basic_memory_buffer<char, 250> MessageBuffer;
-			fmt::vformat_to(fmt::appender(MessageBuffer), Format, Args);
-			ZEN_LOG(m_Log, LogLevel, "{}", std::string_view(MessageBuffer.data(), MessageBuffer.size()));
+			m_Log->Log(Point, Args);
 		}
 	}
 
@@ -47,7 +46,7 @@ public:
 	}
 	virtual void SetLogOperationProgress(uint32_t StepIndex, uint32_t StepCount) override
 	{
-		const size_t PercentDone = StepCount > 0u ? gsl::narrow<uint8_t>((100 * StepIndex) / StepCount) : 0u;
+		[[maybe_unused]] const size_t PercentDone = StepCount > 0u ? gsl::narrow<uint8_t>((100 * StepIndex) / StepCount) : 0u;
 		ZEN_OPERATION_LOG_INFO(*this, "{}: {}%", m_LogOperationName, PercentDone);
 	}
 	virtual uint32_t	 GetProgressUpdateDelayMS() override { return 2000; }
@@ -59,13 +58,14 @@ public:
 private:
 	LoggerRef	m_Log;
 	std::string m_LogOperationName;
+	LoggerRef	Log() { return m_Log; }
 };
 
 void
 StandardLogOutputProgressBar::UpdateState(const State& NewState, bool DoLinebreak)
 {
 	ZEN_UNUSED(DoLinebreak);
-	const size_t PercentDone =
+	[[maybe_unused]] const size_t PercentDone =
 		NewState.TotalCount > 0u ? gsl::narrow<uint8_t>((100 * (NewState.TotalCount - NewState.RemainingCount)) / NewState.TotalCount) : 0u;
 	std::string Task = NewState.Task;
 	switch (NewState.Status)