wip: Define Disc using inductive identity

[aathn]

Description

Redefines the morphisms of discrete categories to be inductive identities instead of paths, to improve computational behaviour.

Checklist

Before submitting a merge request, please check the items below:

• I've read the contributing guidelines.
• The imports of new modules have been sorted with support/sort-imports.hs (or nix run --experimental-features nix-command -f . sort-imports).
• All new code blocks have "agda" as their language.

If your change affects many files without adding substantial content, and
you don't want your name to appear on those pages (for example, treewide
refactorings or reformattings), start the commit message and PR title with chore:.

[Lavenza]

Pull request preview

Changed pages

• Cat.Instances.Discrete (+58, -104)

[plt-amy]

@aathn Thanks! (Un?)fortunately I ended up finishing this pull request while reviewing it. I cherry-picked your commit into #619.

[aathn]

That's great! 😄