This PR was merged into the 4.2-dev branch.

Discussion
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[Messenger] Fix typos

| Q             | A
| ------------- | ---
| Branch?       | 4.2 <!-- see below -->
| Bug fix?      | no
| New feature?  | no <!-- don't forget to update src/**/CHANGELOG.md files -->
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no <!-- don't forget to update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets | N/A   <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        | N/A

Just small typos extracted from #29166 in case it doesn't make it to 4.2.

Commits
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7e763f9 [Messenger] Fix typos

This PR was merged into the 4.2-dev branch.

Discussion
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[Messenger] Add handled & sent stamps

| Q             | A
| ------------- | ---
| Branch?       | 4.2 <!-- see below -->
| Bug fix?      | no
| New feature?  | yes <!-- don't forget to update src/**/CHANGELOG.md files -->
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no <!-- don't forget to update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets | N/A   <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        | symfony/symfony-docs/issues/10661

Based on #29159

This new feature marks sent and handled messages, so middleware can act upon these and use the handler(s) result(s).
This is also the base of a next PR (#29167), introducing a query bus built on top of the message bus.

I'm not sure yet about the best way to determine the handlers and senders names/descriptions to store in the stamps:
- Handlers are callable. I've just reused the [console text descriptor](https://github.com/nicolas-grekas/symfony/blob/1c1818b87675d077808dbf7e05da84c2e1ddc9f8/src/Symfony/Bundle/FrameworkBundle/Console/Descriptor/TextDescriptor.php#L457-L491) format for now.
- ~~Sender are `SenderInterface` instances. `\get_class` is used for now, but a single message can be sent by multiple senders, including of the same class.~~ => Updated. Yielding the sender name if provided, the FQCN otherwise.

~~Instead, what about allowing to yield names from locators, and fallback on the above strategies otherwise? So we'll use transport names from the config for senders, and pre-computed compile-time handlers descriptions?~~
=> Done. For handlers, computing it at compile time might not be straightforward. Let's compute it lazily from `HandledStamp::fromCallable()`

---

### From previous conversations:

> What about not adding HandledStamp on `null` returned from handler

IMHO, `null` still is a result. The stamps allows to identify a message as being handled regardless of the returned value, so makes sense on its own and keeping would require one less check for those wanting to consume it.

> What about adding SentStamp?

Makes sense to me and I think it was requested by @Nyholm before on Slack.
So, included in this PR.

> Should it target 4.2 or 4.3?

Targeting 4.2, because of the removal of the handler result forwarding by middleware. A userland middleware could have used this result, typically a cache middleware. Which would now require extra boring code in userland. This will simplify it and allow users to create their query bus instance until 4.3.

Commits
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2f5acf7 [Messenger] Add handled & sent stamps