refactor: apply clippy auto-fixes (162 warnings resolved)

- Fix needless borrows and references
- Collapse nested if statements
- Replace manual strip_prefix with str::strip_prefix()
- Remove redundant closures in map/unwrap_or_else
- Use Iterator::next_back() instead of rev().next()
- Simplify map_or patterns
- Use std::io::Error::other() instead of new(ErrorKind::Other, ..)
- Use div_ceil() instead of manual ceiling division
- Consolidate format! string arguments
- Various other idiomatic Rust improvements

39 files changed, 220 insertions(+), 320 deletions(-)

src/application/adapters/caldav_adapter.rs

@@ -360,9 +360,9 @@ impl CalDavAdapter {
         for (name, value) in &calendar.custom_properties {
             // Skip properties that start with _ - they're internal
             if !name.starts_with('_') {
-                xml_writer.write_event(Event::Start(BytesStart::new(&format!("CS:{}", name))))?;
+                xml_writer.write_event(Event::Start(BytesStart::new(format!("CS:{}", name))))?;
                 xml_writer.write_event(Event::Text(BytesText::new(value)))?;
-                xml_writer.write_event(Event::End(BytesEnd::new(&format!("CS:{}", name))))?;
+                xml_writer.write_event(Event::End(BytesEnd::new(format!("CS:{}", name))))?;
             }
         }