Update MSRV to Rust 1.70.0 (#3310)

* Update to Rust 1.70

* Fix renamed clippy lint

* Use let-else more

* Code cleanup

* Remove derelict Safety comments

* Enable more clippy lints

crates/egui_plot/src/axis.rs

@@ -255,9 +255,8 @@ impl AxisWidget {
 
             // --- add ticks ---
             let font_id = TextStyle::Body.resolve(ui.style());
-            let transform = match self.transform {
-                Some(t) => t,
-                None => return response,
+            let Some(transform) = self.transform else {
+                return response;
             };
 
             for step in self.steps.iter() {

crates/egui_plot/src/items/mod.rs

@@ -1,4 +1,5 @@
 //! Contains items that can be added to a plot.
+#![allow(clippy::type_complexity)] // TODO(emilk): simplify some of the callback types with type aliases
 
 use std::ops::RangeInclusive;