Provide cached project-root names combinators (cached!)

[ChrisPenner]

Overview

• Starts the move to using Names and PPEs at the project scope
• Removes global fallbacks for these PPEs, which may lead to hashes if a project isn't properly self-contained, but also avoids huge delays and weird name suffix-qualification from loading names from who-knows-where.
• Makes it much easier to get the names/ppe you actually want (e.g. the project root names with or without transitive libs)
• Caches names/ppes by branch hash to avoid re-computing huge names objects on every command invocation. Can cache up to 4 project-branches at a time currently to avoid thrashing.

After this change, in most cases we'll now use project-root names, even when you're cd'd into a project sub-namespace. If you're not in a project it'll continue to use your current namespace.

E.g. if you do unison/base/main data.List> view map it'll pretty print map with the PPE from the root of unison/base/main , which includes all your dependencies, since this is what you wanted anyways :man-shrugging:

Using the same PPE during your whole project workflow like this also allows us to cache those names per-project branch rather than re-computing them on every command loop which we do right now 😬

Implementation notes

• Adds a GLOBAL BranchHash -> BranchNames cache which can be used by the CLI and the LSP to avoid re-computing the names for a given branch all the time.
• Provides new combinators for getting project names and PPEs, see projectRootNames[WithoutTransitiveLibs], projectRootPPED[WithoutTransitiveLibs], and uses these as the default basicNames helper.

Interesting/controversial decisions

Might be a few gotchas to sort out (like there always is when we switch our PPE behaviour), but I think it's worth moving towards this mode.

Test coverage

Existing transcripts mostly cover this, but I'll add one to prove we use the project-root ppe even when in a sub-namespace.

Loose ends

Some open questions would be what to do when the user specifically requests something outside of your project (e.g. view .blah.foo ) and which PPE to use if the user cd's into a lib dependency, but I think we can find good answers for those.