Add regression tests for zero-speed segment updates

[afarber]

Issue

Add Cucumber scenarios to verify that closing segments via --segment-speed-file doesn't incorrectly block turns at unrelated intersections or cascade to parallel routes.

Also add a unit test documenting the turn_id uniqueness invariant and improves the turn penalty warning log.

Tasklist

• CHANGELOG.md entry (How to write a changelog entry)
• update relevant Wiki pages
• add tests (see testing documentation)
• review
• adjust for comments

Requirements / Relations

Related to #7332

[Copilot]

Pull request overview

Fixes incorrect routing/turn behavior when closing segments via --segment-speed-file during MLD customization, attributed to concurrent turn-penalty updates.

Changes:

• Add mutex-based synchronization around a turn-penalty write during parallel edge updates in the updater.
• Add Cucumber scenarios covering “closure shouldn’t cascade” routing regressions.
• Add an Unreleased changelog entry for the fix.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
src/updater/updater.cpp	Introduces mutex/lock guard around a turn_weight_penalties update during tbb::parallel_for.
features/testbot/zero-speed-updates.feature	Adds regression scenarios to ensure closures don’t block turns at unrelated intersections or cascade to parallel routes.
CHANGELOG.md	Adds an Unreleased entry describing the fix.

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[afarber]

Hi, I misunderstood how tbb::parallel_for with blocked_range works and have reverted the mutex.

I have updated the PR title and description and feel free to close if not useful.