fix(vfs): harden getdirentries and APR filepath resolution (#77)

* fix(vfs): defer host cursor commit in getdirentries

Follow-up VFS hardening task applying the same guest-writes-first discipline established in the time subsystem to directory enumeration.

Deferred Commit in KernelGetdirentriesCore:

- Reordered guest output so the 512-byte dirent buffer is written first via TryWriteCompat, basep is updated second (when non-null) via TryWriteUInt64Compat, and directory.NextIndex is advanced only after both guest writes succeed.

- Removed the early basep write at method entry that could mutate guest memory before buffer validation and advance the host cursor before a successful dirent delivery, causing permanent entry loss on MEMORY_FAULT at bufferAddress.

- EOF handling: when currentIndex >= Entries.Length, write basep with the final offset and return 0 without mutating NextIndex, matching FreeBSD getdirentries(2) semantics and preventing infinite retry loops.

KernelGetdents path: basePointerAddress is passed as 0, so the transaction collapses to buffer write then host cursor advance with no basep side effect.

Out of scope: coalesced {id, size} writes in sceKernelAprResolveFilepathsToIdsAndFileSizes; NetCtl connected-state stubs.

Files: KernelMemoryCompatExports.cs

* fix(vfs): resolve-first bulk commit in APR filepath resolution

Refactored sceKernelAprResolveFilepathsToIdsAndFileSizes to stop writing ids and sizes into guest memory one element at a time.

- Removed the uint.MaxValue placeholder write at the start of each loop iteration.

- Path resolution and file size lookup now fill host-side buffers first; on EFAULT or NOT_FOUND the guest ids/sizes arrays are left untouched.

- ids and sizes are packed into contiguous byte buffers and written with one TryWriteCompat call per output array instead of separate TryWriteUInt32Compat / TryWriteUInt64Compat per index.

- AmprFileRegistry.Register is called only after guest writes succeed.

- AmprFileRegistry.ComputeFileId is internal so ids can be computed without registering paths during the resolve loop.

Files: KernelMemoryCompatExports.cs, AmprFileRegistry.cs

src/SharpEmu.Libs/Ampr/AmprFileRegistry.cs

@@ -21,7 +21,7 @@ internal static class AmprFileRegistry
         return _hostPathsById.TryGetValue(id, out hostPath!);
     }
 
-    private static uint ComputeFileId(string guestPath)
+    internal static uint ComputeFileId(string guestPath)
     {
         var bytes = System.Text.Encoding.UTF8.GetBytes(guestPath);