[23847] Protect DataReaderInstance alive_writers attribute

[juanlofer-eprosima]

Description

This PR attempts to solve the data race produced in intraprocess scenario, when a writer sends a message from a thread (which updates its associated instance state in the reader receiving the message: DataReaderImpl::on_new_cache_change_added → DataReaderHistory::update_instance_nts → … → DataReaderInstance::writer_set), while from another thread the instances state of the same reader is also updated without protection (e.g., when destroying a matched writer: DataReaderImpl::update_subscription_matched_status → … → DataReaderInstance::writer_unregister). In the first thread the reader mutex is taken before calling update_instance_nts, the problem is that in the second thread that mutex is never taken.

Contributor Checklist

• Commit messages follow the project guidelines.
• The code follows the style guidelines of this project.
• Tests that thoroughly check the new feature have been added/Regression tests checking the bug and its fix have been added; the added tests pass locally
• N/A Any new/modified methods have been properly documented using Doxygen.
• N/A Any new configuration API has an equivalent XML API (with the corresponding XSD extension)
• Changes are backport compatible: they do NOT break ABI nor change library core behavior.
• Changes are API compatible.
• N/A New feature has been added to the versions.md file (if applicable).
• N/A New feature has been documented/Current behavior is correctly described in the documentation.
• Applicable backports have been included in the description.

Reviewer Checklist

• The PR has a milestone assigned.
• The title and description correctly express the PR's purpose.
• Check contributor checklist is correct.
• If this is a critical bug fix, backports to the critical-only supported branches have been requested.
• Check CI results: changes do not issue any warning.
• Check CI results: failing tests are unrelated with the changes.

[mergify]

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