Fix localtime/1 mem leak

[petermm]

Fixes #2062

replicate:

  def myloop do
    :erlang.localtime("CET-1CEST,M3.5.0,M10.5.0/3")
    |> IO.inspect()

    :timer.sleep(100)

    :erlang.system_info(:esp32_free_heap_size)
    |> IO.inspect()

    myloop()
  end

And see rapidly decreasing free memory - solution inspired by espressif/esp-idf#9764

Currently in draft, as I believe there is some issue with setting the tz to "" on generic_unix - which means it is set to utc, just need to understand that or guard it..

These changes are made under both the "Apache 2.0" and the "GNU Lesser General
Public License 2.1 or later" license terms (dual license).

SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later

[bettio]

This is a non trivial issue and I'm investigating a fix as well.