chore: move bitfield library to lib director

I'd presonally prefer to use a git submodule here but It doesn't quite
seem like git submodules are possible for individual files. I'll have to
check with FlorenceOS every once and a while to ensure that there are no
lingering soundness issues with the library.

Thanks to @N00byEdge for this wonderful library!

build.zig

@@ -12,6 +12,10 @@ pub fn build(b: *std.build.Builder) void {
     const mode = b.standardReleaseOptions();
 
     const exe = b.addExecutable("zba", "src/main.zig");
+
+    // Bitfield type from FlorenceOS: https://github.com/FlorenceOS/
+    exe.addPackage(.{ .name = "bitfield", .path = .{ .path = "./lib/util/bitfield.zig" } });
+
     exe.setTarget(target);
     exe.setBuildMode(mode);
     exe.install();

lib/util/bitfield.zig

@@ -1,5 +1,3 @@
-// source + credit: https://github.com/FlorenceOS/Florence/blob/master/lib/util/bitfields.zig --
-
 const std = @import("std");
 
 fn PtrCastPreserveCV(comptime T: type, comptime PtrToT: type, comptime NewT: type) type {

src/cpu.zig

@@ -1,6 +1,6 @@
 const std = @import("std");
 const util = @import("util.zig");
-const bitfield = @import("util/bitfield.zig");
+const bitfield = @import("bitfield");
 
 const Bus = @import("bus.zig").Bus;
 const Scheduler = @import("scheduler.zig").Scheduler;