feat: respect `/etc/timezone`, `/etc/localtime`, `TZ` like `ls` and `exa` does

Being used to the `ls` output and having used `exa` which reproduced it (in my opinion) correctly, I believe there is a bug in the `eza` output.
In the examples below you can see how the modification date of the `baz` file is shown differently in `eza`, as if it did not take into account the daylight savings time changes during the year.
The time that is shown **is not incorrect**, it is simply shown in the current timezone (`UTC+1`) instead of taking into account the time changes present in the selected timezone (`Europe/Rome` in this case).

```log
$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 20.04.6 LTS
Release: 20.04
Codename: focal

$ uname -a
Linux pcname 5.4.0-166-generic #183-Ubuntu SMP Mon Oct 2 11:28:33 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux

$ cat /etc/timezone
Europe/Rome
```

```log
$ ls --version
ls (GNU coreutils) 8.30

$ ls -lAF --full-time
total 0
-rw-r--r-- 1 user group 0 2023-02-04 10:35:00.000000000 +0100 bar
-rw-r--r-- 1 user group 0 2023-06-04 10:35:00.000000000 +0200 baz
-rw-r--r-- 1 user group 0 2023-11-12 10:35:00.000000000 +0100 foo
```

```log
$ exa --version
v0.10.1 [+git]

$ exa -aglF --time-style full-iso
.rw-r--r-- 0 user group 2023-02-04 10:35:00.000000000 +0100 bar
.rw-r--r-- 0 user group 2023-06-04 10:35:00.000000000 +0200 baz
.rw-r--r-- 0 user group 2023-11-12 10:35:00.000000000 +0100 foo
```

```log
$ eza --version
v0.15.3 [+git]

$ eza -aglF --time-style full-iso
.rw-r--r-- 0 user group 2023-02-04 10:35:00.000000000 +0100 bar
.rw-r--r-- 0 user group 2023-06-04 09:35:00.000000000 +0100 baz
.rw-r--r-- 0 user group 2023-11-12 10:35:00.000000000 +0100 foo
```