feat: coPset, gset, and namespace infrastructure for invariant masks (PR A)

[hxrts]

Add the data structures and resource algebras needed for invariant mask reasoning in the base logic (wsat, fancy updates). Includes CoPset/GSet types with set operations, CoPsetDisj/GSetDisj disjoint-union CMRAs, hierarchical namespaces with nclose, and PORTING.md updates.

Description

Briefly describe your changes, and link any issues if appropriate.

Fixes # (issue number)

Checklist

• My code follows the mathlib naming and code style conventions
• I have updated PORTING.md as appropriate
• I have added my name to the authors section of any appropriate files

[hxrts]

I probably need to remove the flake.nix from this PR but waiting till the end because git needs to see the nix flake for the environment to work.