Enable the clippy::std_instead_of_core lint (#8394)

Prefer `core::` over `std::` where either work

* Part of https://github.com/emilk/egui/issues/5735

crates/egui_glow/examples/pure_glow.rs

@@ -5,7 +5,7 @@
 #![expect(clippy::undocumented_unsafe_blocks)]
 #![expect(unsafe_code)]
 
-use std::num::NonZeroU32;
+use core::num::NonZeroU32;
 use std::sync::Arc;
 
 use egui_winit::winit;
@@ -146,7 +146,7 @@ impl GlutinWindowContext {
         self.gl_surface.swap_buffers(&self.gl_context)
     }
 
-    fn get_proc_address(&self, addr: &std::ffi::CStr) -> *const std::ffi::c_void {
+    fn get_proc_address(&self, addr: &core::ffi::CStr) -> *const core::ffi::c_void {
         use glutin::display::GlDisplay as _;
         self.gl_display.get_proc_address(addr)
     }
@@ -154,7 +154,7 @@ impl GlutinWindowContext {
 
 #[derive(Debug)]
 pub enum UserEvent {
-    Redraw(std::time::Duration),
+    Redraw(core::time::Duration),
 }
 
 struct GlowApp {
@@ -162,7 +162,7 @@ struct GlowApp {
     gl_window: Option<GlutinWindowContext>,
     gl: Option<Arc<glow::Context>>,
     egui_glow: Option<egui_glow::EguiGlow>,
-    repaint_delay: std::time::Duration,
+    repaint_delay: core::time::Duration,
     clear_color: [f32; 3],
 }
 
@@ -173,7 +173,7 @@ impl GlowApp {
             gl_window: None,
             gl: None,
             egui_glow: None,
-            repaint_delay: std::time::Duration::MAX,
+            repaint_delay: core::time::Duration::MAX,
             clear_color: [0.1, 0.1, 0.1],
         }
     }

crates/egui_glow/src/painter.rs

@@ -55,10 +55,10 @@ impl TextureWrapModeExt for egui::TextureWrapMode {
 #[derive(Debug)]
 pub struct PainterError(String);
 
-impl std::error::Error for PainterError {}
+impl core::error::Error for PainterError {}
 
-impl std::fmt::Display for PainterError {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+impl core::fmt::Display for PainterError {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
         write!(f, "OpenGL: {}", self.0)
     }
 }
@@ -219,7 +219,7 @@ impl Painter {
             let a_tc_loc = gl.get_attrib_location(program, "a_tc").unwrap();
             let a_srgba_loc = gl.get_attrib_location(program, "a_srgba").unwrap();
 
-            let stride = std::mem::size_of::<Vertex>() as i32;
+            let stride = core::mem::size_of::<Vertex>() as i32;
             let buffer_infos = vec![
                 vao::BufferInfo {
                     location: a_pos_loc,

crates/egui_glow/src/shader_version.rs

@@ -2,7 +2,7 @@
 #![expect(clippy::unwrap_used)] // TODO(emilk): avoid unwraps
 #![expect(unsafe_code)]
 
-use std::convert::TryInto as _;
+use core::convert::TryInto as _;
 
 /// Helper for parsing and interpreting the OpenGL shader version.
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]

crates/egui_glow/src/winit.rs

@@ -104,8 +104,8 @@ impl EguiGlow {
 
     /// Paint the results of the last call to [`Self::run`].
     pub fn paint(&mut self, window: &winit::window::Window) {
-        let shapes = std::mem::take(&mut self.shapes);
-        let mut textures_delta = std::mem::take(&mut self.textures_delta);
+        let shapes = core::mem::take(&mut self.shapes);
+        let mut textures_delta = core::mem::take(&mut self.textures_delta);
 
         #[expect(clippy::iter_over_hash_type)] // Order doesn't matter here
         for (id, image_deltas) in textures_delta.set.drain() {