feat: added "serde" feature flag for bones_ecs (#438)

There were existing of `#[cfg_attr(feature = "serde",
derive(serde::Serialize, serde::Deserialize))]` lines already (f.e. on
Entity struct), but serde feature flag itself was missing from
bones_ecs.

Also added `cfg_attr(feature = "serde") ...` line to Entities and
BitSetVec so Entities struct can be serialized.

framework_crates/bones_ecs/Cargo.toml

@@ -14,6 +14,7 @@ keywords.workspace      = true
 default = ["derive", "keysize16"]
 derive  = ["dep:bones_ecs_macros"]
 glam    = ["dep:glam", "dep:paste", "bones_schema/glam"]
+serde   = ["dep:serde"]
 
 keysize16 = []
 keysize20 = []
@@ -33,6 +34,7 @@ bitset-core = "0.1"
 thiserror   = "1.0"
 glam        = { version = "0.24", optional = true }
 paste       = { version = "1.0", optional = true }
+serde       = { version = "1", features = ["derive"], optional = true }
 once_map    = "0.4.12"
 
 [dev-dependencies]

framework_crates/bones_ecs/src/bitset.rs

@@ -43,6 +43,7 @@ pub(crate) const BITSET_SLICE_COUNT: usize = BITSET_SIZE / (32 * 8 / 8);
 
 /// The type of bitsets used to track entities in component storages.
 /// Mostly used to create caches.
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 #[derive(Deref, DerefMut, Clone, Debug)]
 pub struct BitSetVec(pub Vec<[u32; 8]>);
 

framework_crates/bones_ecs/src/entities.rs

@@ -55,6 +55,7 @@ impl Default for Entity {
 ///
 /// It also holds a list of entities that were recently killed, which allows to remove components of
 /// deleted entities at the end of a game frame.
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 #[derive(Clone, HasSchema)]
 pub struct Entities {
     /// Bitset containing all living entities