install: keep post-copy finalization bound to created file

[parasol-aser]

Fixes #12062.

This keeps install bound to the file it actually created instead of reopening the destination by pathname during post-copy finalization.

What changed:

• add O_NOFOLLOW | O_EXCL to fd-based destination creation
• keep the destination file open through finalization
• run --strip-program, chmod, chown, and timestamp updates against that file handle
• fail if the destination pathname no longer resolves to the same file before success
• add a regression test for the symlink-swap --strip-program case

Validation:

• cargo +1.93.0-x86_64-unknown-linux-gnu build -p uu_install --bin install
• cargo +1.93.0-x86_64-unknown-linux-gnu test --test tests --features 'install chmod' test_install::test_install_and_strip_with_program_hyphen -- --exact --nocapture
• cargo +1.93.0-x86_64-unknown-linux-gnu test --test tests --features 'install chmod' test_install::test_install_strip_program_symlink_swap_does_not_touch_victim -- --exact --nocapture

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/install/basic-1. tests/install/basic-1 is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/install/install-C-selinux. tests/install/install-C-selinux is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/install/install-Z-selinux. tests/install/install-Z-selinux is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/install/strip-program. tests/install/strip-program is passing on 'main'. Maybe you have to rebase?
Skipping an intermittent issue tests/date/date-locale-hour (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tail/tail-n0f (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/printf/printf-surprise is now passing!
Skip an intermittent issue tests/cut/bounded-memory (was skipped on 'main', now failing)

[oech3]

Is it able to use rustix instead?

[parasol-aser]

Swapped this over to rustix in c62d1d0 and re-ran the two targeted install tests; both pass.

[oech3]

Please cargo fmt and clippy.