feat(rapier_testbed): autosave testbed configuration + add support for per-example settings (#799)

* feat(rapier_testbed): autosave testbed configuration + add support for per-example parameters

* feat(rapier_testbed): also save the camera position

* feat(rapier_testbed): improve ergonomics of example-specific settings

* chore: cargo fmt

* chore(rapier_testbed): small UI ergonomics improvement

* chore(rapier_testbed): clippy fixes

crates/rapier_testbed3d/Cargo.toml

@@ -57,6 +57,7 @@ bincode = "1"
 md5 = "0.7"
 Inflector = "0.11"
 serde = { version = "1", features = ["derive"] }
+serde_json = "1"
 bevy_egui = "0.31"
 bevy_ecs = "0.15"
 bevy_core_pipeline = "0.15"
@@ -77,6 +78,7 @@ bevy = { version = "0.15", default-features = false, features = [
     "bevy_render",
     "bevy_pbr",
     "bevy_gizmos",
+    "serialize"
 ] }
 
 # Dependencies for WASM only.