Expand API coverage, add Resource wrapper, error subclasses, tooling

[Kaevan89]

Expand API coverage, add Resource wrapper, error subclasses, tooling

Brings the SDK to feature parity with veryfi-python (minus CLI), adds a
lightweight Hash-compatible response wrapper, splits errors by HTTP status,
refreshes tooling and dependencies, and gets the suite to 100% line
coverage on lib/.

Bumps to 4.0.0. The 4.x line is non-breaking for existing 3.x callers
because Veryfi::Resource is a subclass of Hash and the new error
subclasses all inherit from Veryfi::Error::VeryfiError — existing
response["id"] access and rescue Veryfi::Error::VeryfiError calls keep
working unchanged.

== New API coverage ==

• Any Document (A-Docs): client.any_document.* (incl. async)
• Bank Statement: client.bank_statement.* (incl. async)
• Bank Statement Split: client.bank_statement_split.*
• Business Card: client.business_card.*
• Check: client.check.* (incl. async and remittance)
• Classify: client.classify.*
• PDF Split: client.pdf_split.*
• Tax Lines: client.tax_line.*
• W-2 / W-8 BEN-E / W-9: client.w2., .w8., .w9.*
• W-2 Split: client.w2_split.*
• Extensions: document.process_bulk, document_tag.add_multiple /
  document_tag.replace, line_item.delete_all, and per-resource tag
  operations on every processed-document resource via a TagOperations
  mix-in.

== Veryfi::Resource — lightweight response wrapper ==

API responses are now Veryfi::Resource objects (a subclass of Hash)
that support BOTH access styles equivalently:

response["id"]                          # works (Hash compat)
response[:id]                           # symbol keys too
response.id                             # attribute access
response.vendor.name                    # nested
response.line_items.first.total         # recursive wrapping of arrays
response.is_duplicate?                  # ? predicate sugar
JSON.pretty_generate(response)          # serializes identically

Nested hashes are wrapped recursively, arrays of hashes become arrays of
Resources, leaf values pass through. Unknown keys raise NoMethodError so
typos surface immediately instead of silently returning nil. #to_h
returns a recursively-unwrapped plain Hash on demand.

== Error model ==

• Fix: Veryfi::Error::VeryfiError now calls super(@message) instead of
  super(message), so error.full_message and the rest of Exception
  machinery see the same string error.message returns.
• Add HTTP-status subclasses, all inheriting from VeryfiError:
  BadRequest (400), Unauthorized (401), AccessLimitReached (403),
  NotFound (404), RequestTimeout (408), Conflict (409),
  UnsupportedMediaType (415), TooManyRequests (429),
  ClientError (other 4xx), ServerError (5xx).
• Every error exposes #status, #response and #message.

== Configuration + custom Faraday ==

• Veryfi.configure { |c| ... } + Veryfi.client for process-wide
  singletons (Rails-style). Veryfi.reset! for tests.
• Veryfi::Client.new accepts a faraday: lambda that runs against the
  Faraday::Connection before first use, so users can attach retries,
  persistent connections, logging, or any middleware without us bundling
  extra deps.

== Dependencies ==

• Drop runtime dep on activesupport (only used for strip_heredoc in one
  spec — replaced with squiggly heredoc).
• Bump faraday constraint to >= 2.14.1, < 3.0 to clear CVE-2026-25765.
  Faraday 2.x requires Ruby >= 3.0, so the gem's required_ruby_version
  was raised to >= 3.0 and the Gemfile no longer needs the per-Ruby
  conditional pin — the gemspec is the single source of truth.
• json updated to 2.19.5 to clear CVE-2026-33210.
• bundle-audit is now clean on Ruby 3.0, 3.4 and 4.0.

== Tooling ==

• Add Rakefile with rake spec, rake rubocop, rake yard, rake ci.
• Add .yardopts (powers https://veryfi.github.io/veryfi-ruby/).
• .rubocop.yml: add rubocop-rake plugin, set SuggestExtensions: false,
  bump Metrics/ParameterLists max to 8 for the new faraday: kwarg, and
  pin TargetRubyVersion: 3.0 so cop behaviour is identical across the
  whole 3.0 → 4.0 CI matrix.
• CI matrix updated to ["3.0", "3.1", "3.2", "3.3", "3.4", "4.0"]
  (drops EOL Ruby 2.7, adds Ruby 4.0 stable).
• .ruby-version bumped to 3.4.1 for local development parity.
• Add dev-deps: yard, rubocop-rake.

== Internals ==

• Replace 17 copy-pasted memoized accessors in Veryfi::Client with an
  api_namespace :document, Veryfi::Api::Document DSL — wiring a new
  API class is now a single line.
• Normalize HTTP headers in Veryfi::Request to all-string keys for
  cleaner Faraday middleware integration.

== Docs ==

README rewrite:

• Fix outdated install (~> 0.1 → ~> 4.0).
• New "Versioning & compatibility" section, including a supported-Ruby
  table covering 3.0 through 4.0.
• New "Response objects" section.
• New "Common parameters & defaults" section enumerating file_path /
  file_url / categories / tags / auto_delete / boost_mode / async /
  external_id / max_pages_to_process / bounding_boxes /
  confidence_details with defaults, required-ness and meanings.
• New "Configuring the client" + "Custom Faraday configuration".
• New "Handling errors" with the full error-class table.
• Per-endpoint usage examples for every new resource.

YARD doc blocks on every public method across all 16 API classes
(descriptions, @see links, @param / @option with defaults, @return).

== Tests ==

• spec/fixtures/ reorganized into:
  spec/fixtures/files/
  spec/fixtures/responses//.json
• New response_fixture_body / file_fixture_path helpers remove
  hardcoded paths from every spec.
• New spec files for every new API class, Veryfi::Resource,
  Veryfi.configure/.client, and error subclasses.
• New end-to-end resource_wrapping_integration_spec.rb sweeps every
  API namespace and asserts that response["id"], response[:id] and
  response.id all return the same value via the real Request pipeline.

== Verification ==

Ruby	Environment	rspec	rubocop	bundle-audit
3.0.7	Docker ruby:3.0.7 (CI parity)	205 examples, 0 failures	53 files, no offenses	clean
3.4.1	rbenv (arm64-darwin)	205 examples, 0 failures	53 files, no offenses	clean
4.0.5	rbenv (arm64-darwin)	205 examples, 0 failures	53 files, no offenses	clean

100% line coverage on lib/.