ref(managed): Add Managed::zip function

[pierceroberts]

#5985

Added a generic Managed::merge helper that consumes two managed values and returns a single Managed<(T, S)>,
transferring outcome responsibility into the merged wrapper while preserving metadata from the first value.

Also added a unit test covering the new behavior: the merged value retains both inner values, emits outcomes
for both through the first managed handle when dropped, and prevents the second managed value from emitting
duplicate outcomes after the merge.

I also ran:

• pre-commit --files
• cargo test -p relay-server:

test result: ok. 383 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.67s

• also ran the new test individually:

   cargo test --package relay-server --lib --all-features -- managed::managed::tests::test_merge_into_tuple --exact --nocapture 

    Finished `test` profile [unoptimized] target(s) in 0.78s
     Running unittests src/lib.rs (target/debug/deps/relay_server-ca0b589ee2561a09)

running 1 test
test managed::managed::tests::test_merge_into_tuple ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 406 filtered out; finished in 0.00s

Legal Boilerplate

Look, I get it. The entity doing business as "Sentry" was incorporated in the State of Delaware in 2015 as Functional Software, Inc. and is gonna need some rights from me in order to utilize my contributions in this here PR. So here's the deal: I retain all rights, title and interest in and to my contributions, and by keeping this boilerplate intact I confirm that Sentry can use, modify, copy, and redistribute my contributions, under Sentry's choice of terms.

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[pierceroberts]

Alright I got the main pipelines to pass @Dav1dde and I made the changes. Let me know what you think! Thanks.
It does look like there are some integration tests for python that are failing silently:

requests.exceptions.ConnectionError: Connection refused by Responses - the call doesn't match any registered mock.

https://github.com/getsentry/relay/actions/runs/27785392311/job/82223873618?pr=6088#step:7:166

[Dav1dde]

Thanks, looks great!

Documenting the behaviour of what happens to the meta is important to me to make it clear it's not an oversight or "random", the debug_assert is useful because we should never merge two Managed instances from different origins.

[Dav1dde]

Changed the title to make the CI check happy

[pierceroberts]

@Dav1dde , I believe I have added the assert check and a test. Give it another look and let me know! Thanks.

[Dav1dde]

We basically only do debug_assert!'s in this module, would stick to the same pattern here.

[pierceroberts]

Sounds good, I can change this.

[Dav1dde]

Untested, shouldn't debug_assert_eq!(first.scoping(), second.scoping()) work here?

[pierceroberts]

I'll try it. But yes, probably. Simpler is usually better 😄

[Dav1dde]

Thanks! I think only a make format is missing before CI is happy.

[pierceroberts]

Yeah super weird, I think the rust-analyzer locally is conflicting with the make style-rust lint-rust version. So I have had to some tweaking. Just re-ran it 🤞