Freeze registries at startup, when everything has been registered

[Al2Klimov]

to query them at runtime lock-freely.

[julianbrost]

@Al2Klimov I'd suggest you to answer the questions in the previous review first before requesting another review.

[Al2Klimov]

Done.

[yhabteab]

While you're touching all the classes anyway, please remove the first template parameter from Registry, it's just useless and isn't requried by that class to function correctly.

EDIT: Also, please rebase the PR, so that the GHAs run successfully.

[yhabteab]

Looks fine to me now, although I'm confused with the verboseness of the commits.