Rust: Implement herb-analysis crate based on Rubydex

[marcoroth]

This pull request adds a herb-analysis crate that brings Herb's cross-file static analysis to Rust, backed by rubydex.

It started as a spike to evaluate rubydex as a resolution backend and has grown into a full port of the Herb::Analysis namespace, including an actionview command set that mirrors the Ruby CLI subcommands.

Motivation

#1667 implements Action View template dependency analysis in Ruby. Its weakest part is helper and constant resolution: scan_helpers! flat-scans every def in app/helpers/**/*.rb, so it misses gem-provided helpers, misses helpers reaching the view through included concerns, and records constants as a naive "#{receiver}.#{name}" with no namespace resolution. That drives the unknown_calls warnings.

rubydex indexes the analysed app and the gems in its Gemfile.lock, and walks real ancestor chains. The question worth answering was what that enables in Rust that Ruby cannot reach, and the answer turned out to be most of the warning noise.

What the crate provides

The binary exposes two command families. The first are rubydex-backed introspection commands:

helpers    [path] [--only app,gem,rails,route] [--roots A,B]   what a template can call, grouped by origin
audit      [path] [--gem G]                                    cross-check the Action View helper registry
ancestors  <Name> [path] [--built-ins]                         ancestor chain and completeness
constants  [NAME] [--nesting A::B] [path]                      list constants, or resolve one
stats      [path]                                              counts and per-phase timings

helpers reconstructs everything a template in an arbitrary Rails app can call. It resolves gems from Gemfile.lock across all three source types (registry, git checkouts including monorepo subdirectories, and path sources), discovers helper modules by the include_all_helpers convention that no static index can infer from code, walks ActionView::Base for the built-ins, reads helper_method declarations off controllers, and derives route helpers from config/routes.rb.

The second family ports the Ruby herb actionview subcommands:

check         [path]           check render calls and flag unresolved partials
graph         [path]           show the render graph for a project
dependencies  <file>           show a template's dependency manifest
flow          <file> <state>   trace one piece of state through every partial it reaches
context       <partial>        show what a partial is rendered inside of
signature     <partial>        show the strict locals a partial receives

Behind them sit Rust counterparts for PartialResolution, PartialIndex, PartialDeclaration, RenderGraph, ProjectIndex, TemplateDependencies, StateFlow, and RubyLocalsIndex, so the three implementations now share one architecture.

Where Rust goes further than Ruby

Both check commands print the same sections, in the same order, with the same wording. The counts differ, and that difference is the point, Rust resolves names Ruby's scan cannot see.

	Ruby	Rust
Checked	232 files	232 files
Renders	515 total, 477 with partial, 4 dynamic, 38 other	same
Partials	265 on disk, 4 unresolved	265 on disk, 4 unresolved
Unknown calls	108	45

Measured against rubyevents. The remaining Rust figure is dominated by four ui_* helpers that a component library generates by convention.

check output gained three things on both sides:

• Locals that cannot be inferred is its own section. When no call site contributes a single local name, either because nothing renders the partial or because its callers pass locals opaquely through **locals, there is no signature to learn from. Reporting those as missing methods was misleading.
• Unknown method calls end with a tally of the most frequent names, since the same name usually recurs across many templates.
• The summary breaks the warning categories out and reports how many component templates were skipped.

 Summary:
  Checked      232 files
  Renders      515 total | 477 with partial | 4 dynamic | 38 other
  Partials     265 on disk | 4 unresolved | 14 unused
  Warnings     47 undeclared locals | 44 uninferable locals | 1 instance variable | 45 unknown calls
  Ignored      6 component templates in app/components/

Related #1667

[github-actions]

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