Process inline RBS comments natively without the require-hook rewriter

[paracycle]

Summary

• Tapioca's pipeline now reads inline #: / # @... RBS comments directly from source instead of relying on a load-time rewriter that produced sig {} blocks at boot.
• Removes lib/tapioca/rbs/rewriter.rb, the require-hooks dependency, the bootsnap shim, dsl --only-bootsnap-rbs-cache, and the TAPIOCA_RBS_CACHE plumbing. No more Bootsnap iseq cache to manage.
• The gem pipeline always builds a Rubydex::Graph (seeded with core/stdlib RBS) so constants in inline sigs can be resolved to their fully-qualified names. A matching path on the DSL side picks up #: sigs for arbitrary host-app methods.

Why

The require-hook rewriter rewrote every .rb file at load time so sorbet-runtime would track #: comments as sig {} blocks. It worked, but it forced require-hooks into the dependency tree, made boot slower, and shipped its own bootsnap iseq cache so large apps could survive the cost. With Tapioca now able to parse RBS straight from source (via Rubydex), all of that goes away.

What changed

New modules under lib/tapioca/rbs/

• comments.rb — parses a stream of [comment_string, line] tuples (as obtained from Rubydex's Definition#comments) into signatures and annotations classified into class-level / method-level groups.
• type_qualifier.rb — walks an RBI::Type tree and emits a fully-qualified string. User constants resolve through a Rubydex graph (so Bar inside Foo becomes ::Foo::Bar); Sorbet's own T:: constants are prefixed with ::T::; user-defined generics (Sorbet T::Generic) are resolved but emitted without a leading :: to match Sorbet's runtime serializer convention.
• dsl_signatures.rb — DSL-side RBS lookup. Builds a per-process Rubydex graph from the host workspace + already-loaded source files + core/stdlib RBS, looks up declarations by qualified name (or by source location for anonymous classes built with Class.new), and synthesizes an RBI::Sig. Lexical nesting for anonymous classes is recovered via a small Prism visitor.

Gem pipeline (lib/tapioca/gem/...)

• Pipeline builds the graph unconditionally (previously only when include_doc: true) and exposes gem_graph, rbs_comments_for_constant, and rbs_comments_for_method.
• Listeners::Methods + MethodNodeAdded carry an optional Pipeline::RBSMethodLookup when no Sorbet runtime sig was found.
• Listeners::SorbetSignatures synthesizes a sig from the RBS lookup when present (with attr-vs-method-vs-overload handling and method-level annotations).
• Listeners::SorbetHelpers picks up # @abstract, # @final, # @sealed, # @interface.
• Listeners::SorbetRequiredAncestors picks up # @requires_ancestor:.
• Listeners::SorbetTypeVariables picks up class-level #: [A, B] (with variance / upper: / fixed: blocks).
• Listeners::Documentation filters Rubydex definitions down to ones inside the gem so the now-always-on graph doesn't leak core-RBS docs.

DSL pipeline (lib/tapioca/dsl/...)

• Dsl::Compiler#compile_method_*_to_rbi falls back to DslSignatures.build when no Sorbet runtime sig is registered. Compiler itself now explicitly extend T::Generic and declares ConstantType = type_member.
• ActiveModelTypeHelper.type_for also falls back to RBS comments for deserialize / cast / cast_value / serialize.

Cleanup

• Deletes lib/tapioca/rbs/rewriter.rb, sorbet/rbi/shims/bootsnap.rbi, sorbet/rbi/gems/require-hooks@0.4.0.rbi.
• Drops require-hooks from tapioca.gemspec and Gemfile.lock.
• Removes dsl --only-bootsnap-rbs-cache and the related CLI / command code.
• Removes the "Rewriting RBS comments to Sorbet signatures" + "Caching rewrites with Bootsnap" + "Priming the cache from CI" sections from the README, replacing them with a short "Inline RBS comments" note.
• internal.rb keeps Module.include(T::Sig) so bare sig {} calls in user/gem code (and our specs) still work without extend T::Sig.

Test status

bin/test runs 788 tests with 0 failures, 0 errors, 2 pre-existing skips.

A couple of tests had to move with the design:

• spec/tapioca/runtime/reflection_spec.rb now uses a real sig { ... } instead of relying on the rewriter to translate #: -> String to a runtime sig.
• spec/tapioca/gem/pipeline_spec.rb updates the T.proc / T::Array[::String] / requires_ancestor { Kernel } expectations to the new ::T and ::Kernel qualification convention.
• spec/tapioca/cli/dsl_spec.rb drops the bootsnap- and --only-bootsnap-rbs-cache-specific tests, renames the "preserves RBS comment rewriting" case to "exposes inline RBS method signatures to DSL compilers", and broadens a Ruby-version-sensitive stack trace regex.