fix: allow deserializing BDAddr from non-borrowed strings

[icewind1991]

ran into this while trying to use DBAddr as a value in a toml map.

Trying to deserialize a toml like

"00:11:22:33:44:55" = "Test"

into a HashMap<BDAddr, String>

results in the error

Error: TOML parse error at line 5, column 1
  |
5 | "00:11:22:33:44:55" = "Test"
  | ^^^^^^^^^^^^^^^^^^^
invalid type: string "00:11:22:33:44:55", expected A colon seperated Bluetooth address, like `00:11:22:33:44:55`

By making the Visitor also handle owned and ephemeral strings the deserialization works as expected.