refactor: drop dead code and use the standard library where it already does the job (#76)

No behaviour change.

- Deleted, unused or one-line wrappers: panes.RuneIndexes, Detail.Refresh (SetDescribed does it), SecretValue.Len, Query.Empty, Clipboard.Native, config.Load, get's value, Model.done, providerOf (cachefile.ProviderOf), contextWithTimeout, searchCoverage, startCrawl, showKeybindings, the expiry aliases and daysLeft.
- cmp.Or instead of the two cmpOr copies; slices.Sorted(maps.Keys(…)), maps.Copy, wg.Go, utf8.RuneCountInString and new(true) instead of loops and helpers that do the same.
- A container's pane title is set once, not twice; a redundant length check in share links and a no-op assignment in linkhandler.Launch are gone.
- Tests call ansi.Strip and lastLines directly; gofmt -s on links.go.

Reviewed-on: #76
Co-authored-by: Karl-Einar Bergstrøm <karl-einarb@outlook.com>

internal/ui/app/cache.go

@@ -66,7 +66,7 @@ func (m *Model) refreshShown(before []provider.Object) tea.Cmd {
 	if i < 0 || sameListing(before[i], s) {
 		return nil
 	}
-	m.detail.Refresh(s)
+	m.detail.SetDescribed(s)
 	uncache(m, m.cache.details, detailKey(s))
 	return m.describe(s)
 }