style: crank clippy to pedantic+nursery and fix all lints

Enable the full clippy all + pedantic + nursery groups as workspace warnings,
with a small documented allow-list for the pedantic/nursery lints this project
intentionally does not follow (rustdoc-style requirements, deliberate numeric
casts in the protocol/UI layers, and a few noisy nursery lints). Also enable
the rust unused_lifetimes and unsafe_op_in_unsafe_fn lints.

Fixed every resulting warning (527 -> 0) mechanically per clippy's suggestions:
inline format args, const fns, item ordering, let-else, redundant clones,
map_or, cast_lossless, Eq derives, associated-fn conversions for methods that
never used self, and removing unnecessary Result wrappers whose call sites could
never propagate an error. No runtime behavior changed; cargo fmt applied.

cargo clippy --workspace --all-targets: 0 warnings. All tests pass.

soulseek-rs/src/ui/styles.rs

@@ -71,11 +71,11 @@ pub fn unfocused_border_style() -> Style {
     Style::default()
 }
 
-pub fn focused_border_type() -> BorderType {
+pub const fn focused_border_type() -> BorderType {
     BorderType::Rounded
 }
 
-pub fn unfocused_border_type() -> BorderType {
+pub const fn unfocused_border_type() -> BorderType {
     BorderType::Rounded
 }
 
@@ -88,7 +88,7 @@ pub fn border_style(focused: bool) -> Style {
     }
 }
 
-pub fn border_type(focused: bool) -> BorderType {
+pub const fn border_type(focused: bool) -> BorderType {
     if focused {
         focused_border_type()
     } else {
@@ -100,9 +100,7 @@ pub fn border_type(focused: bool) -> BorderType {
 pub fn format_shortcuts(shortcuts: &[(&str, &str)]) -> String {
     shortcuts
         .iter()
-        .map(|(key, action)| {
-            format!("[{} {} {}]", key, HIGHLIGHT_SYMBOL, action)
-        })
+        .map(|(key, action)| format!("[{key} {HIGHLIGHT_SYMBOL} {action}]"))
         .collect::<Vec<_>>()
         .join(" ")
 }
@@ -124,7 +122,7 @@ pub fn format_shortcuts_styled(shortcuts: &[(&str, &str)]) -> Line<'static> {
                 .add_modifier(Modifier::BOLD),
         ));
         spans.push(Span::styled(
-            format!(" {} ", HIGHLIGHT_SYMBOL),
+            format!(" {HIGHLIGHT_SYMBOL} "),
             dimmed_style(),
         ));
         spans.push(Span::raw(action.to_string()));
@@ -165,7 +163,7 @@ pub fn format_progress_bar(
         Span::raw("]"),
         Span::raw(" "),
         Span::styled(
-            format!("{}%", percentage),
+            format!("{percentage}%"),
             primary_style()
                 .add_modifier(Modifier::BOLD)
                 .fg(Color::default()),