Logging and diagnostics improvements (#941)

Core logging and system diagnostics improvements, extracted from the compute branch.

### Logging
- **Elapsed timestamps**: Console log now shows elapsed time since launch `[HH:MM:SS.mmm]` instead of full date/time; file logging is unchanged
- **Short level names**: 3-letter short level names (`trc`/`dbg`/`inf`/`wrn`/`err`/`crt`) used by both console and file formatters via `ShortToStringView()`
- **Consistent field order**: Standardized to `[timestamp] [level] [logger]` across both console and file formatters
- **Slim LogMessage/LogPoint**: Remove redundant fields from `LogMessage` (derive level/source from `LogPoint`), flatten `LogPoint` to inline filename/line fields, shrink `LogLevel` to `int8_t` with `static_assert(sizeof(LogPoint) <= 32)`
- **Remove default member initializers** and static default `LogPoint` from `LogMessage` — all fields initialized by constructor
- **LoggerRef string constructor**: Convenience constructor accepting a string directly
- **Fix SendMessage macro collision**: Replace `thread.h` include in `logmsg.h` with a forward declaration of `GetCurrentThreadId()` to avoid pulling in `windows.h` transitively

### System Diagnostics
- **Cache static system metrics**: Add `RefreshDynamicSystemMetrics()` that only queries values that change at runtime (available memory, uptime, swap). `SystemMetricsTracker` snapshots full `GetSystemMetrics()` once at construction and reuses cached topology/total memory on each `Query()`, avoiding repeated `GetLogicalProcessorInformationEx` traversal on Windows, `/proc/cpuinfo` parsing on Linux, and `sysctl` topology calls on macOS

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