deps: replace abandoned tempdir with tempfile

[FredPhilipy]

FIx #4162

Replace abandoned tempdir with actively maintained tempfile

• Update dependencies in 3 Cargo.toml files: tempdir 0.3.7 → tempfile 3.8
• Update API usage in test and benchmark code:
  • tempdir::TempDir::new("name") → tempfile::TempDir::new()
  • into_path() → path()
• Affects only test and benchmark code, no production impact
• All tests pass (105 trie tests + storage tests)