Pkg: Add fs/README.md to document performance & security improvements

Signed-off-by: Michael Mayer <michael@photoprism.app>

pkg/fs/buffer_pool.go

@@ -0,0 +1,24 @@
+package fs
+
+import "sync"
+
+// copyBufferSize defines the shared buffer length used for large file copies/hashes.
+const copyBufferSize = 256 * 1024
+
+// copyBufferPool reuses byte slices to reduce allocations during file I/O.
+var copyBufferPool = sync.Pool{ //nolint:gochecknoglobals // shared pool for I/O buffers
+	New: func() any {
+		buf := make([]byte, copyBufferSize)
+		return &buf
+	},
+}
+
+// getCopyBuffer returns a pooled buffer for copy operations.
+func getCopyBuffer() []byte {
+	return *(copyBufferPool.Get().(*[]byte))
+}
+
+// putCopyBuffer returns a buffer to the pool.
+func putCopyBuffer(buf []byte) {
+	copyBufferPool.Put(&buf)
+}