Generalize middleware options to per-class Options Data value objects

[ericproulx]

Summary

Following the per-feature VersionOptions / RescueOptions work in #2712 and #2716, middlewares that want typed option accessors now declare a per-class Options = Data.define(…). Middleware::Base routes the kwargs through it on init and exposes both a frozen Hash (options, back-compat) and the typed Data instance (config).

Mechanism

Middleware::Base#initialize, when the subclass declares an Options constant (ancestor search included so subclasses like Versioner::Path inherit Versioner::Base::Options):

• builds @config = self.class::Options.new(**options)
• sets @options = @config.to_h.freeze (frozen Hash view of the Data, for legacy options[:key] callers)

Subclasses without an Options constant (Filter, Auth::*) continue to flow through the legacy DEFAULT_OPTIONS Hash + deep_merge path unchanged.

Converted middlewares

• Middleware::Formatter (5 fields).
• Middleware::Error (14 fields). rescue_options: defaults to Grape::DSL::RescueOptions.new; an explicit nil (passed by Endpoint#error_middleware_options when no rescue_from was called) is coerced to the default in the Data's initialize.
• Middleware::Versioner::Base (7 fields). Adds content_types: / format: so the PrecomputedContentTypes mixin's accessor reads land cleanly. version_options: defaults to Grape::DSL::VersionOptions.new.

Each Options field list, def_delegators :config, and Options#initialize kwarg list is alphabetic.

Back-compat surface

• attr_reader :options still returns a frozen Hash representation of the Data (config.to_h.freeze) for converted middlewares. Subclasses that read options[:key] keep working.
• DEFAULT_OPTIONS is restored as Options.new.to_h.freeze on each converted middleware so existing references resolve. Marked @deprecated in the YARD comment; will be removed in a future release.
• Options#[] is defined on each Data class as a Hash-style shim that emits a deprecation warning via Grape.deprecator and forwards to the named accessor. Any code that reaches into the Data with [:key] gets a migration nudge.

Contract change (documented in UPGRADING)

Passing an unknown kwarg to a converted middleware now raises ArgumentError instead of being silently swallowed by **options. One formatter spec was passing rescue_options: (dead weight; Formatter doesn't read it) — dropped.

That stricter contract is exactly what made version_options / rescue_options cleaner in their respective PRs.

Test plan

• bundle exec rspec — 2313 examples, 0 failures
• bundle exec rubocop lib/grape/middleware/ — clean
• CI green

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