adds a version struct helper

[Absolucy]

this adds a new proc macro for auxtools, #[versioned], used for having "versioned" internal structs - basically, it automatically implements the BytecodePre1630 and BytecodePost1630 stuff:

#[versioned(
	Pre1630 if crate::version::BYOND_VERSION_MINOR <= 1627,
	Post1630,
)]
#[repr(C)]
pub struct ProcMetadata {
	#[only_in(Post1630)]
	unk_2: u32,
	pub bytecode: misc::BytecodeId,
	pub locals: misc::LocalsId,
	pub parameters: misc::ParametersId
}

// ...

#[versioned(
	Pre516 if crate::version::BYOND_VERSION_MAJOR < 516,
	Post516,
)]
#[repr(C)]
struct ProcInstanceInner {
	#[only_in(Post516)]
	unk_pre: u32,
	pub args_count: u32,
	pub args: *mut values::Value,
	#[only_in(Pre516)]
	unk_3: [u8; 0x58],
	#[only_in(Post516)]
	unk_4: [u8; 0x58],
	pub time_to_resume: u32
}

some part of me is thinking there's still a better way to do this, but i can't quite figure out how to describe it tbh

also i fixed a random clippy lint in list.rs that was annoying me