build(deps): upgrade allocator-api2 to 0.3

See the projects README for the reasons for removing the nightly feature:
https://github.com/zakarumych/allocator-api2/tree/2873b737304003b1cf0c999f4148497293cc9e0f#usage

Author: mkroening

Cargo.lock

@@ -14,7 +14,7 @@ all-features = true
 rustdoc-args = ["--cfg", "docsrs"]
 
 [dependencies]
-allocator-api2 = { version = "0.2", default-features = false, features = ["alloc"], optional = true }
+allocator-api2 = { version = "0.3", default-features = false, features = ["alloc"], optional = true }
 bitfield-struct = "0.11"
 bitflags = "2"
 endian-num = { version = "0.2", features = ["bitflags", "linux-types"] }
@@ -28,6 +28,6 @@ zerocopy-derive = { version = "0.8", optional = true }
 [features]
 alloc = ["dep:allocator-api2"]
 mmio = []
-nightly = ["allocator-api2/nightly"]
+nightly = []
 pci = ["dep:pci_types"]
 zerocopy = ["dep:zerocopy", "dep:zerocopy-derive", "endian-num/zerocopy"]

Cargo.toml

@@ -1,6 +1,14 @@
 use ::alloc::alloc::handle_alloc_error;
-use allocator_api2::alloc::{AllocError, Allocator, Global};
-use allocator_api2::boxed::Box;
+#[cfg(feature = "nightly")]
+use ::alloc::{
+    alloc::{AllocError, Allocator, Global},
+    boxed::Box,
+};
+#[cfg(not(feature = "nightly"))]
+use allocator_api2::{
+    alloc::{AllocError, Allocator, Global},
+    boxed::Box,
+};
 
 use super::*;