Remove unnecessary #[allow(...)] annotations (#6870)

* Remove unnecessary `#[allow]` annots

Reduce the number of lint exceptions that are not necessary with the
current state of the code (or more recent toolchain)

* Remove dead code from `FileStructure` in nu-command

* Replace `allow(unused)` with relevant feature switch

* Deal with `needless_collect` with annotations

* Change hack for needless_collect in `from json`

This change obviates the need for `allow(needless_collect)`
Removes a pessimistic allocation for empty strings, but increases
allocation size to `Value`

Probably not really worth it.

* Revert "Deal with `needless_collect` with annotations"

This reverts commit 05aca98445.

The previous state seems to better from a performance perspective as a
`Vec<String>` is lighter weight than `Vec<Value>`

crates/nu-glob/src/lib.rs

@@ -863,7 +863,6 @@ fn chars_eq(a: char, b: char, case_sensitive: bool) -> bool {
 }
 
 /// Configuration options to modify the behaviour of `Pattern::matches_with(..)`.
-#[allow(missing_copy_implementations)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Default)]
 pub struct MatchOptions {
     /// Whether or not patterns should be matched in a case-sensitive manner.