Add tempdir support

crates/lb/tests/fs.lua

@@ -0,0 +1,17 @@
+local ok, fs = pcall(require, "lb:fs")
+if not ok then return end
+
+describe("temp files", function()
+  test("temp_dir cleans itself", function()
+    local path
+    do
+      local dir = fs:temp_dir()
+      path = dir:path()
+      assert(path and path ~= "")
+      fs:write(path .. "/test.txt", "test file")
+      assert(fs:read(path .. "/test.txt") == "test file")
+    end
+    collectgarbage()
+    assert(not pcall(fs.read, fs, path .. "/test.txt"))
+  end)
+end)