fix: only extract active wrapper during spawn

[passcod]

Fixes #19

Noting this is a breaking change due to changing

pub fn get_wrap<W: $wrapper + 'static>(&self) -> Option<&W>

to

pub fn get_wrap<W: $wrapper + 'static>(&self) -> Option<::std::cell::Ref<W>>

There might be a way to revert that change and/or not expose the Ref but I can't see it right now.

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Reading list

• https://docs.rs/process-wrap/latest/x86_64-pc-windows-msvc/src/process_wrap/std/job_object.rs.html
• https://docs.rs/process-wrap/latest/x86_64-pc-windows-msvc/src/process_wrap/std/creation_flags.rs.html
• https://microsoft.github.io/windows-docs-rs/doc/windows/Win32/System/Threading/constant.CREATE_SUSPENDED.html
• https://doc.rust-lang.org/stable/std/cell/struct.Ref.html#method.clone
• https://github.com/watchexec/process-wrap/blob/main/src/generic_wrap.rs