Fix Test::Future::Deferred weak lifetime handling

[fglock]

Summary

• Preserve returned reference scalars and closure capture owners so weak/refcount-sensitive Future and Test::Future::Deferred flows keep live referents alive only as long as Perl would.
• Avoid capturing shadowed lexicals and avoid refcounting List::Util pair helper temporaries as local bindings.
• Keep Sub::Quote/Moo weak metadata alive while still releasing ordinary unblessed callback captures, and guard overload stringification when an overload returns another scalar wrapper for the same referent.

Unit coverage

• Future-style callback cleanup for unblessed captured guards.
• Sub::Quote deferred constructor metadata used by Moo overloaded coderef generation.
• Broken string overload returning the invocant, matching the DBIx::Class txn recursion shape.
• Returned owned scalar and List::Util pair helper refcount cases from the Test::Future::Deferred failure chain.

Testing

• timeout 1200 make
• timeout 600 jperl -Iblib/lib -Iblib/arch t/01future-pp.t in Future-0.52 build
• timeout 600 jperl -Iblib/lib -Iblib/arch t/02cancel-pp.t in Future-0.52 build
• timeout 7200 ./jcpan -t Test::Future::Deferred
• timeout 7200 ./jcpan -t Moo
• timeout 7200 ./jcpan -t DBIx::Class passed on rerun (Files=314, Tests=13120, Result: PASS)

Note: an earlier DBIx::Class full run had a one-off TAP harness no-output timeout in t/sqlmaker/bind_transport.t; the file passed directly in 9s and the full DBIx::Class rerun passed.