Fix comment style: add space after // (#8333)

## Summary

- [x] I have followed the instructions in the PR template

Fixes comment-style violations of the `CONTRIBUTING.md` code style rule:

> `// Comment like this.` and not `//like this`

### Files changed

- `crates/epaint/src/shapes/bezier_shape.rs`: `//temporary solution` →
`// temporary solution`, and 22× `//add the start point` → `// add the
start point`
- `crates/egui/src/animation_manager.rs`: `//start new animation…` → `//
start new animation…`
- `crates/eframe/src/web/web_painter_wgpu.rs`:
`//create_new.instance_descriptor…` → `//
create_new.instance_descriptor…`

No code logic changes — only adding the missing space after `//` in
inline and standalone comments.

## Test plan

- [x] `cargo fmt --check`
- [x] `cargo clippy -p epaint -p egui`
- [x] `cargo test -p epaint --lib`

crates/egui/src/animation_manager.rs

@@ -95,7 +95,7 @@ impl AnimationManager {
                     anim.from_value..=anim.to_value,
                 );
                 if anim.to_value != value {
-                    anim.from_value = current_value; //start new animation from current position of playing animation
+                    anim.from_value = current_value; // start new animation from current position of playing animation
                     anim.to_value = value;
                     anim.toggle_time = input.time;
                 }