Explicitly delete copy constructors for classes with Poco::NObserver

[rboston628]

Description of work

Poco v1.15 (published to anaconda.org on 2026-02-17) introduces std::atomic into NObserver, which secretly prevents copying of any class with an NObserver object in it. You can only find this out when you go to build on Windows with MSVC and learn it is trying to create a default copy constructor, leading to an error.

This was discovered while making release candidates for mantid v6.15. As pin as added in 6.15 to enable the package build in PR #40957.

The problem is caused in classes with a NObserver member variable, but without an explicit copy constructor. The MSVC compiler will attempt to create defaults, which is an error. This work deletes the copy constructors in these classes, so that the defaults will not be constructed.

To test:

Run a build with a pin in Poco 1.15.

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[github-actions]

👋 Hi, @rboston628,

Conflicts have been detected against the base branch. Please rebase your branch against the base branch.