all: Add some generics and incorporate them into the codebase.

[Shaptic]

PR Checklist

PR Structure

• This PR has reasonably narrow scope (if not, break it down into smaller PRs).
• This PR avoids mixing refactoring changes with feature changes (split into two PRs
  otherwise).
• This PR's title starts with name of package that is most changed in the PR, ex.
  services/friendbot, or all or doc if the changes are broad or impact many
  packages.

Thoroughness

• This PR adds tests for the most critical parts of the new functionality or fixes.
• I've updated any docs (developer docs, .md
  files, etc... affected by this change). Take a look in the docs folder for a given service,
  like this one.

Release planning

• I've updated the relevant CHANGELOG (here for Horizon) if
  needed with deprecations, added features, breaking changes, and DB schema changes.
• I've decided if this PR requires a new major/minor version according to
  semver, or if it's mainly a patch change. The PR is targeted at the next
  release branch if it's not a patch change.

What

Adds and incorporates a generic Min/Max rather than customs ones per-type and per-package.

Why

blessed generics

Known limitations

There might be other places we're doing this inline that are much harder to find, e.g.

if a < b {
    a = b
}

one-offs that didn't warrant a dedicated min for that package.

[leighmcculloch]

generics is a reasonably generic name. Given that this package contains functions that work with ordered types, how about we named it ordered?

[Shaptic]

The idea was to expand it over time to include other helpers (as you can tell from my ambitious branch naming). Min/Max are the most obvious offenders, but now that I've added and incorporated a Set[T any] container, would you reconsider the rename? 😉

[Shaptic]

I also plan to add both

func mapKeys[T any, U any](m map[T]U) []T      // and
func mapValues[T any, U any](m map[T]U) []U

once this gets merged into the lighthorizon branch.

[leighmcculloch]

I'd put the map functions into a collections/map package, and the Set type into a collections/set package. i.e.

ordered
collections/set
collections/map

[leighmcculloch]

This is a small detail and I defer to you. It's great we can do these things now 🎉.

[Shaptic]

I guess my goal was to keep everything in its own subfolder (with no explicit reason besides it being a 1.18+ feature and the general satisfaction of keeping a PR in a single folder), but I do like these names! Done in 4d58a36.

[leighmcculloch]

👏🏻

[leighmcculloch]

This is a small detail and I defer to you. It's great we can do these things now 🎉.