feat: add global --r-bin cli argument

[JosiahParry]

This PR closes #447.

It works by adding a new --r-bin argument that adding a new RCommandLookup::Explicit variant which, when provided, will (fallibly) create an RInstall from the binary path.

Default behavior:

When specifying bin path:

Note that it properly creates the 4.6 subdirectory in addition to the default 4.5 version

waiting ⚡ ll rv/library
total 0
drwxr-xr-x@ 4 josiahparry  staff   128B May  5 10:40 .
drwxr-xr-x@ 5 josiahparry  staff   160B May  5 10:33 ..
drwxr-xr-x@ 3 josiahparry  staff    96B May  5 10:35 4.5
drwxr-xr-x@ 3 josiahparry  staff    96B May  5 10:40 4.6

[JosiahParry]

I'm unsure how to create proper integration tests for this. If guidance can be provided would be happy to :)

[dpastoor]

i think directionally this is fine - there is one bit of nuance i want to check around if we need to also do any RHOME or other shenanigans, but between a couple codex/claude risk assessment prompts i will push it through this weekend we can get this in

[Copilot]

Pull request overview

Adds support for selecting an explicit R binary from the CLI (intended to enable workflows like rv sync using a caller-provided R installation path, per #447) by introducing a new RCommandLookup::Explicit mode and wiring it through CLI context creation.

Changes:

• Add global --r-bin CLI flag and plumb it into Context::new(...) for sync-like commands.
• Introduce RCommandLookup::Explicit(RInstall) and update Context initialization to accept a pre-resolved RInstall.
• Add RInstall::try_from_bin(...) helper to construct an RInstall from a binary path.
• Add .zed/settings.json editor configuration file.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 7 comments.

File	Description
src/r_finder.rs	Adds RInstall::try_from_bin helper to construct an install from an explicit binary path.
src/context.rs	Adds RCommandLookup::Explicit(RInstall) and updates context initialization flow to use it.
src/main.rs	Introduces global --r-bin flag and passes explicit lookup into several command contexts.
.zed/settings.json	Adds Zed editor settings (not directly related to --r-bin).

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[JosiahParry]

As indicated by #451 (comment) it's not clear how to do this.

[JosiahParry]

This is a fundamental misunderstanding of the rv codebase becuase RCommandLookup::Skip doesn't mean "doesn't use R" it means "use R from the path.

RCommandLookup::Skip => RInstall::default_from_path(),

[JosiahParry]

I've reviewed Codex's review and I think it fundamentally misunderstands this PR.

I'm happy to remove the .zed settings if requested. I view this to be akin to the existing .vscode/ folder. Without it developing in Zed will require updating the .zed settings every time a new PR is done—which, I can understand.

Regarding integration tests, if some guidance can be provided that would be great:
#451 (comment)

[dpastoor]

keeping the zed piece is fine - i agree it gives people using that editor the right LSP base