LS: Fix duplicated and misplaced diagnostics

[Arcticae]

The diagnostics were not sorted properly, because of lack of including their kind in sorting before deduplication
(.format() is a derivative of that)

Also added a check for file relevance, so that vfs-based diagnostics aren't included in the mapping phase

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This change is 

[mkaput]

Reviewed 3 of 3 files at r1, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @Arcticae, @Draggu, @orizi, and @piotmag769)

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crates/cairo-lang-diagnostics/src/diagnostics.rs line 335 at r1 (raw file):

        let files_db = db.upcast();
        let mut indexed_dup_diagnostic =
            diagnostic_with_dup.iter().enumerate().sorted_by_key(|(idx, diag)| {

if you're opting for heavy weapons here, then consider using https://docs.rs/itertools/latest/itertools/trait.Itertools.html#method.sorted_by_cached_key0

[mkaput]

Reviewed 1 of 1 files at r2, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @Draggu, @orizi, and @piotmag769)