Enhance DiskFS initialization and error handling

- Updated `disk.New` to support asynchronous initialization for large caches, improving responsiveness during startup.
- Introduced an eviction function parameter to `disk.New`, ensuring proper handling of over-capacity scenarios.
- Enhanced error handling in various components, including memory and disk tests, to ensure robustness and clarity.
- Refactored tests to validate new behaviors, including checks for delayed attachment and proper error propagation.
- Removed obsolete error handling code and tests related to the now-deleted errors package, streamlining the codebase.

vfs/eviction/eviction_test.go

@@ -15,7 +15,10 @@ func TestGetEvictionFunction_Default(t *testing.T) {
 		t.Fatal("default eviction fn nil")
 	}
 	// Should be LRU
-	m := memory.New(1024)
+	m, err := memory.New(1024)
+	if err != nil {
+		t.Fatal(err)
+	}
 	// create something to evict
 	w, _ := m.Create("f", 100)
 	w.Write(make([]byte, 100))
@@ -28,7 +31,10 @@ func TestGetEvictionFunction_Default(t *testing.T) {
 
 func TestEvictLRU_Delegates(t *testing.T) {
 	t.Parallel()
-	m := memory.New(1024)
+	m, err := memory.New(1024)
+	if err != nil {
+		t.Fatal(err)
+	}
 	w, _ := m.Create("f1", 1000) // > cap - needed to force
 	w.Write(make([]byte, 1000))
 	w.Close()
@@ -55,14 +61,20 @@ func TestEviction_StrategiesAndDispatch(t *testing.T) {
 	}
 	for _, c := range cases {
 		t.Run(c.name, func(t *testing.T) {
-			m := memory.New(2048)
+			m, err := memory.New(2048)
+			if err != nil {
+				t.Fatal(err)
+			}
 			w, _ := m.Create(fmt.Sprintf("e%04d", 1), 1500)
 			w.Write(make([]byte, 1500))
 			w.Close()
 			_ = c.fn(m, 100)
 			// disk path too (no real fs ops needed for dispatch)
 			td := t.TempDir()
-			d := disk.New(td, 2048)
+			d, err := disk.New(td, 2048, nil)
+			if err != nil {
+				t.Fatal(err)
+			}
 			w2, _ := d.Create(fmt.Sprintf("e%04d", 2), 1500)
 			w2.Write(make([]byte, 1500))
 			w2.Close()