Add EnvironmentLoader for ruby-rbs crate

[dak2]

Summary

Mirrors RBS::EnvironmentLoader: resolves core, library, and explicit-directory sources in Ruby's load order, then parses each .rbs file once into an Environment.

#2954

Architecture differences from RBS::EnvironmentLoader

• Ruby's loader both resolves what to load (gems, versions, manifest dependencies) and reads it.
• The Rust one only reads: it takes resolved directories, so everything needing RubyGems knowledge stays in Ruby, and Rust does the walking, parsing, and interning.
• That drops the dependency machinery, and makes the name pool per-Environment state instead of a process-global one.

	Ruby	Rust
Library resolution	resolves name/version → directory via gem_sig_path / Repository, and expands manifest.yaml dependencies	add_library(name, path) takes an already-resolved directory; no Repository, no manifest expansion, no implicit stringio
Registration API	one add(path:/library:/version:) with keyword modes	add_library / add_dir, the modes separated by type
Duplicate registration	libs is a Set, to stop dependency expansion from recursing	plain Vec; with no expansion, first-wins on seen_files is enough
Name pool	process-global symbols and TypeName objects	Environment owns the Interners, so loaded names stay resolvable for its lifetime
File walk	Pathname.glob("**/*.rbs"), sorted as /-joined strings	recursive read_dir, sorted by platform path; symlinked directories are not followed, and only PermissionDenied / NotFound are skipped

Usage

Register the directories on the loader, then load them into an Environment:

let loader = EnvironmentLoader::new(Some(core_root))
    .add_library("pathname", pathname_sig_dir) // resolved on the Ruby side
    .add_dir(PathBuf::from("sig"));

let env = Environment::from_loader(&loader)?;

for source in env.sources() {
    // source.path, source.kind (Core / Library { name, path } / Dir { path }),
    // source.directives, source.declarations
}

load can also fill an existing Environment, and returns what it read, in the
order it read it:

let mut env = Environment::new();
let loaded: Vec<LoadedFile> = loader.load(&mut env)?; // { path, kind } per file

Notes

• Directories are visited core → libraries → dirs, and a path already read is skipped, so the first source registering a file wins.
• LoadError is Io { path, .. } or Parse { path, message }; the sources read before the failure are already in the Environment.
• The Environment owns the interners, so env.interners() is what resolves and displays the interned names held by the loaded declarations.

Co-Authored-By: Claude Opus 5 (1M context) noreply@anthropic.com

[dak2]

Remove Buffer. In details, 2b3df5a