fix: cargo warnings

[alejandro-vaz]

this PR fixes all cargo warnings

unused unsafe

finally allowed the unsafe which was only unsafe in our MSRV to complain

#[allow(unused_unsafe, reason = "Unsafe in MSRV")]
(unsafe { &raw const self.inline }).cast()

that removes the lint warning

removed use of smallvec! and smallvec_inline!

removed the use in tests.rs of the smallvec! and smallvec_inline! deprecated macros

instead, SmallVec::from and SmallVec::from_buf were used

removed the use of SmallVec::into_inner

removed the use of the now-deprecated into_inner in favor of TryInto::<[T; M]>::into

removed the test for empty macro

self-explanatory. now the macros are deprecated