aio-libs / multidict / 37149148588

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Mark __sizeof__ cold (#1661)

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## What do these changes do?

Marks `multidict_sizeof()`, the C extension's only `__sizeof__` (shared
by `MultiDict` and `CIMultiDict`), as `COLD`. It is not a hot path, and
`_multidict.c` sits at GCC's inlining budget, so it is now compiled for
size instead of inlining helpers into it. The helpers it calls,
`htkeys_sizeof()` and `htkeys_resume_slots_bytes()`, also serve
`md_clone_from_ht()` (the `copy()` path) and the resume-slot allocation,
so they keep their `static inline`. The pure-Python backend has nothing
equivalent.

## Are there changes in behavior for the user?

No.

## Is it a substantial burden for the maintainers to support this?

No; it is a one-word attribute.

## Related issue number

N/A

## Checklist

- [x] I think the code is well written
- [ ] Unit tests for the changes exist (N/A, no behavior change;
existing `__sizeof__` tests cover it)
- [x] Documentation reflects the changes (N/A)
- [ ] If you provide code modification, please add yourself to
`CONTRIBUTORS.txt` (N/A)
- [x] Add a new news fragment into the `CHANGES/` folder
- [x] `make doc-spelling` passes and any new technical words are added
to `docs/spelling_wordlist.txt`

Drafted with Claude Code (Claude Opus 5.5); reviewed by @asvetlov.

<details>
<summary>Agent run details (optional, for reviewers)</summary>

Tests: C extension 3.14.7 `3875 passed, 179 skipped`; C extension
3.10.17 `3879 passed, 175 skipped`; pure Python `--no-c-extensions`
`1508 passed, 24 skipped`.

Inlining: `tools/check_inlining.py` ok on 3.14.7 (16 rules) and 3.14.7t
(18 rules).

Codegen (`tools/codegen_diff.py --ref 467f0964`, clean worktree;
base-to-base control reports 0 functions): `multidict_sizeof` 47 -> 41
instructions on GIL, 67 -> 63 on FT. Other reported functions are layout
only (same instruction count, same call targets) except small shrinks in
`MultiDict_SetDefault` (579 -> 570, GIL), `_str_borrow_identity_ci` and
`... (continued)

791 of 1582 branches covered (50.0%)

Branch coverage included in aggregate %.

9224 of 10068 relevant lines covered (91.62%)

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