core: unify clock dispatch logic, add precise clocks, and enforce coalesced time writes (#71)

Comprehensive refactoring of the system time subsystem to unify clock dispatching, support precise clock extensions, and secure memory boundaries against partial state corruption.

Centralized Clock Dispatch Engine:
- Extracted shared elapsed-tick calculation and clock-routing math into a unified internal static bool ResolveClockTime() dispatch engine under KernelRuntimeCompatExports.cs.
- Moved all clock identifiers from KernelMemoryCompatExports to KernelRuntimeCompatExports as internal const int constants to eliminate cross-file duplication while preserving raw compiler switch-case layout optimizations.
- Added native alias mapping support for CLOCK_REALTIME_PRECISE (9) and CLOCK_MONOTONIC_PRECISE (11).
- Hardened the Orbis sceKernelClockGettime path by routing it through the new dispatcher, resolving a pre-existing logic flaw where any non-zero clock_id incorrectly fell back to monotonic time. Invalid IDs now properly fail with ORBIS_GEN2_ERROR_INVALID_ARGUMENT.

Coalesced Single-Transaction Memory Writes:
- Replaced consecutive isolated 8-byte scalar writes across POSIX clock_gettime, gettimeofday, and Orbis sceKernelClockGettime/sceKernelGettimeofday with safe single-transaction 16-byte stackalloc byte buffer writes via BinaryPrimitives and ctx.Memory.TryWrite. This entirely prevents partial memory state corruption on virtual page boundaries.
- Implemented a single 8-byte coalesced zero-fill transaction for the deprecated/legacy timezone buffer (timezoneAddress != 0), aligning it with standard FreeBSD stub behavior.
- Standardized POSIX failure path routines. Write faults cleanly issue TrySetErrno(ctx, Efault) while safely omitting explicit manual Rax writes, letting the import dispatcher natively sign-extend the return -1 value to 0xFFFFFFFFFFFFFFFF.

Zero-Alloc Host RDTSC Execution Stub:
- Patched CreateRdtscReader() to stream native architecture opcodes out of stack-allocated spans directly into host executable memory zones (VirtualAlloc) via unsafe { Buffer.MemoryCopy(...) }, completely removing the high-frequency .ToArray() runtime allocation overhead on the hot path.

Files: KernelRuntimeCompatExports.cs, KernelMemoryCompatExports.cs

src/SharpEmu.Libs/Kernel/KernelRuntimeCompatExports.cs

@@ -14,6 +14,15 @@ namespace SharpEmu.Libs.Kernel;
 
 public static class KernelRuntimeCompatExports
 {
+    internal const int ClockRealtime = 0;
+    internal const int ClockVirtual = 1;
+    internal const int ClockProf = 2;
+    internal const int ClockMonotonic = 4;
+    internal const int ClockUptime = 5;
+    internal const int ClockRealtimePrecise = 9;
+    internal const int ClockMonotonicPrecise = 11;
+    internal const int ClockRealtimeFast = 10;
+    internal const int ClockMonotonicFast = 12;
     private const int Efault = 14;
     private const ulong TlsErrnoOffset = 0x40;
     private const ulong TlsStackChkGuardBaseOffset = 0x800;
@@ -187,15 +196,9 @@ public static class KernelRuntimeCompatExports
 
         long seconds;
         long nanoseconds;
-        if (clockId == 0)
+        if (!ResolveClockTime(clockId, out seconds, out nanoseconds))
         {
-            var now = DateTimeOffset.UtcNow;
-            seconds = now.ToUnixTimeSeconds();
-            nanoseconds = (now.Ticks % TimeSpan.TicksPerSecond) * 100;
-        }
-        else
-        {
-            GetProcessMonotonicTime(out seconds, out nanoseconds);
+            return (int)OrbisGen2Result.ORBIS_GEN2_ERROR_INVALID_ARGUMENT;
         }
 
         Span<byte> timespecBuffer = stackalloc byte[16];
@@ -632,6 +635,36 @@ public static class KernelRuntimeCompatExports
         return address != 0 && ctx.TryWriteInt32(address, value);
     }
 
+    internal static bool ResolveClockTime(int clockId, out long seconds, out long nanoseconds)
+    {
+        switch (clockId)
+        {
+            case ClockRealtime:
+            case ClockRealtimePrecise:
+            case ClockRealtimeFast:
+            case ClockVirtual:
+            case ClockProf:
+            {
+                var now = DateTimeOffset.UtcNow;
+                seconds = now.ToUnixTimeSeconds();
+                nanoseconds = (now.Ticks % TimeSpan.TicksPerSecond) * 100;
+                return true;
+            }
+
+            case ClockMonotonic:
+            case ClockMonotonicPrecise:
+            case ClockMonotonicFast:
+            case ClockUptime:
+                GetProcessMonotonicTime(out seconds, out nanoseconds);
+                return true;
+
+            default:
+                seconds = 0;
+                nanoseconds = 0;
+                return false;
+        }
+    }
+
     internal static void GetProcessMonotonicTime(out long seconds, out long nanoseconds)
     {
         var elapsedTicks = Stopwatch.GetTimestamp() - _processStartCounter;