Fix clippy warnings

[Mallets]

Fix clippy warnings.

What is left out:

$ cargo +stable clippy --all-features --all-targets --fix --lib -p zenoh-c --allow-dirty
   Compiling zenoh-c v1.2.1 (/Users/luca/Repository/eclipse-zenoh-c)
warning: manually constructing a nul-terminated string
  --> src/config.rs:33:53
   |
33 | pub static Z_CONFIG_MODE_KEY: &c_char = unsafe { &*(b"mode\0".as_ptr() as *const c_char) };
   |                                                     ^^^^^^^^^ help: use a `c""` literal: `c"mode"`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_c_str_literals
   = note: `#[warn(clippy::manual_c_str_literals)]` on by default

warning: manually constructing a nul-terminated string
  --> src/config.rs:36:17
   |
36 |     unsafe { &*(b"connect/endpoints\0".as_ptr() as *const c_char) };
   |                 ^^^^^^^^^^^^^^^^^^^^^^ help: use a `c""` literal: `c"connect/endpoints"`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_c_str_literals

warning: manually constructing a nul-terminated string
  --> src/config.rs:39:17
   |
39 |     unsafe { &*(b"listen/endpoints\0".as_ptr() as *const c_char) };
   |                 ^^^^^^^^^^^^^^^^^^^^^ help: use a `c""` literal: `c"listen/endpoints"`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_c_str_literals

warning: manually constructing a nul-terminated string
  --> src/config.rs:42:17
   |
42 |     unsafe { &*(b"transport/auth/usrpwd/user\0".as_ptr() as *const c_char) };
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use a `c""` literal: `c"transport/auth/usrpwd/user"`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_c_str_literals

warning: manually constructing a nul-terminated string
  --> src/config.rs:45:17
   |
45 |     unsafe { &*(b"transport/auth/usrpwd/password\0".as_ptr() as *const c_char) };
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use a `c""` literal: `c"transport/auth/usrpwd/password"`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_c_str_literals

warning: manually constructing a nul-terminated string
  --> src/config.rs:48:17
   |
48 |     unsafe { &*(b"scouting/multicast/enabled\0".as_ptr() as *const c_char) };
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use a `c""` literal: `c"scouting/multicast/enabled"`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_c_str_literals

warning: manually constructing a nul-terminated string
  --> src/config.rs:51:17
   |
51 |     unsafe { &*(b"scouting/multicast/interface\0".as_ptr() as *const c_char) };
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use a `c""` literal: `c"scouting/multicast/interface"`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_c_str_literals

warning: manually constructing a nul-terminated string
  --> src/config.rs:54:17
   |
54 |     unsafe { &*(b"scouting/multicast/address\0".as_ptr() as *const c_char) };
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use a `c""` literal: `c"scouting/multicast/address"`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_c_str_literals

warning: manually constructing a nul-terminated string
  --> src/config.rs:57:17
   |
57 |     unsafe { &*(b"scouting/timeout\0".as_ptr() as *const c_char) };
   |                 ^^^^^^^^^^^^^^^^^^^^^ help: use a `c""` literal: `c"scouting/timeout"`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_c_str_literals

warning: manually constructing a nul-terminated string
  --> src/config.rs:60:17
   |
60 |     unsafe { &*(b"scouting/delay\0".as_ptr() as *const c_char) };
   |                 ^^^^^^^^^^^^^^^^^^^ help: use a `c""` literal: `c"scouting/delay"`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_c_str_literals

warning: manually constructing a nul-terminated string
  --> src/config.rs:63:17
   |
63 |     unsafe { &*(b"timestamping/enabled\0".as_ptr() as *const c_char) };
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^ help: use a `c""` literal: `c"timestamping/enabled"`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_c_str_literals

warning: manually constructing a nul-terminated string
  --> src/config.rs:66:17
   |
66 |     unsafe { &*(b"transport/shared_memory/enabled\0".as_ptr() as *const c_char) };
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use a `c""` literal: `c"transport/shared_memory/enabled"`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_c_str_literals

warning: `zenoh-c` (lib test) generated 12 warnings
warning: `zenoh-c` (lib) generated 12 warnings (12 duplicates)

In order to fix the above problem, p-avital/validated-struct-macros-rs#2 should be merged and validated-struct-macros-rs be released with updated dependencies.