Allow more than 1024 threads on high-end machines

[robertnurnberg]

This PR changes the maximum value for Threads from the constant 1024 to four times the number of available processors.

This follows some discussion on discord.

No functional change.

[vondele]

I suggest to use
int MaxThreads = std::max(1024, 4 * int(get_hardware_concurrency()));

So we don't 'regress' in the shown number of threads. The constant 4 is fine with me.

[Disservin]

also move it just below the MaxHashMB thanks

[robertnurnberg]

Thanks for the feedback. Implemented both suggestions.

[github-actions]

clang-format 18 needs to be run on this PR.
If you do not have clang-format installed, the maintainer will run it when merging.
For the exact version please see https://packages.ubuntu.com/noble/clang-format-18.

(execution 13864034864 / attempt 1)