feat: persistent islands + manifold reduction (#895)

* feat: initial implementation of contact manifold reduction

* feat: try bepu-like manifold reduction

* feat: simplification of the constraints counting and indexing logic

* feat: add concept of incremental islands with a single awake island

More islands manager fixes

* feat: start adding support for multiple awake islands

* feat: add more timings

* feat: implement incremental island split & merge

* chore: refactor islands manager into multiple files

* chore: refactor manifold reduction to its own file + add naive reduction method

* feat: add islands manager validation checks

* fix various bugs in the new islands system

* chore: remove redundant active_set_offset field

crates/rapier2d-f64/Cargo.toml

@@ -43,6 +43,7 @@ serde-serialize = [
     "dep:serde",
     "bit-vec/serde",
     "arrayvec/serde",
+    "vec_map/serde"
 ]
 enhanced-determinism = ["simba/libm_force", "parry2d-f64/enhanced-determinism"]
 debug-render = []

crates/rapier2d/Cargo.toml

@@ -44,6 +44,7 @@ serde-serialize = [
     "dep:serde",
     "bit-vec/serde",
     "arrayvec/serde",
+    "vec_map/serde"
 ]
 enhanced-determinism = ["simba/libm_force", "parry2d/enhanced-determinism"]
 debug-render = []

crates/rapier3d-f64/Cargo.toml

@@ -46,6 +46,7 @@ serde-serialize = [
     "parry3d-f64/serde-serialize",
     "dep:serde",
     "bit-vec/serde",
+    "vec_map/serde"
 ]
 enhanced-determinism = ["simba/libm_force", "parry3d-f64/enhanced-determinism"]
 debug-render = []

crates/rapier3d/Cargo.toml

@@ -48,6 +48,7 @@ serde-serialize = [
     "parry3d/serde-serialize",
     "dep:serde",
     "bit-vec/serde",
+    "vec_map/serde"
 ]
 enhanced-determinism = ["simba/libm_force", "parry3d/enhanced-determinism"]
 debug-render = []