Replaced the @_cdecl attribute with the @c attribute across the library to update to Swift 6.4.

Sources/PlaydateKit/PlaydateKit.docc/GettingStarted.md

@@ -6,14 +6,14 @@ Bootstrap the bindings from your game's entry point and drive a frame loop.
 
 A Playdate game has a single C entry point, `eventHandler`, which the
 firmware calls with a `PlaydateAPI*` and an event code. Export it with
-`@_cdecl`, call ``Playdate/initialize(with:)`` on the first event, and
+`@c`, call ``Playdate/initialize(with:)`` on the first event, and
 install an update callback:
 
 ```swift
 import CPlaydate
 import PlaydateKit
 
-@_cdecl("eventHandler")
+@c(eventHandler)
 func eventHandler(
     pointer: UnsafeMutableRawPointer,
     event: PDSystemEvent,

Sources/PlaydateKit/Support.swift

@@ -73,7 +73,7 @@ extension String {
 /// The pointer is later released with plain `free`, so it cannot be offset
 /// to adjust alignment; the firmware allocator's natural alignment has to
 /// satisfy the request, which the precondition asserts.
-@_cdecl("posix_memalign")
+@c(posix_memalign)
 public func posix_memalign(
     _ memptr: UnsafeMutablePointer<UnsafeMutableRawPointer?>,
     _ alignment: Int,