chore: remove usages of sort.Sort (#6689)

improve language stats rounding:

- Add tests (I had to omit some edge cases as the current method is
non-determistic in some cases, due to random order of map access).
- Document the algorithm used.
- Lower the amount of calculations that need to be done.
- Because of the aforementioned non-determistic don't use stable sort
and instead regular sort.

better sorting for `RepositoryList`:

- Add testing
- Use `slices.Sortfunc` instead of `sort.Sort`.
- Remove the methods needed for `sort.Sort`.

better git tag sorter:

- Use `slices.SortFunc` instead of `sort.Sort`.
- Remove `tagSorter` and its related methods.
- Added testing.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/6689
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: Gusted <postmaster@gusted.xyz>
Co-committed-by: Gusted <postmaster@gusted.xyz>

models/repo/repo_list.go

@@ -36,18 +36,6 @@ const RepositoryListDefaultPageSize = 64
 // RepositoryList contains a list of repositories
 type RepositoryList []*Repository
 
-func (repos RepositoryList) Len() int {
-	return len(repos)
-}
-
-func (repos RepositoryList) Less(i, j int) bool {
-	return repos[i].FullName() < repos[j].FullName()
-}
-
-func (repos RepositoryList) Swap(i, j int) {
-	repos[i], repos[j] = repos[j], repos[i]
-}
-
 // ValuesRepository converts a repository map to a list
 // FIXME: Remove in favor of maps.values when MIN_GO_VERSION >= 1.18
 func ValuesRepository(m map[int64]*Repository) []*Repository {