v2.0.0

First stable release of the v2 rewrite. Aggregates everything that
landed across the three beta tags — see the entries below for the
detail of each step.

If you're upgrading from v1.x, read UPGRADING.md for
the full migration guide. The legacy Alle_AI\Anthropic\AnthropicAPI
shim still works but emits E_USER_DEPRECATED notices on every call;
it will be removed in v3.0. Set ALLE_AI_ANTHROPIC_FAIL_ON_DEPRECATED=1
during migration to convert deprecations into thrown exceptions.

Highlights since v1.3

• Modern PHP 8.2+ idioms: readonly DTOs, backed enums, attributes.
• AlleAI\Anthropic\Client with PSR-18 / PSR-17 transport, middleware
  stack (auth, user-agent, idempotency, retries with exponential
  backoff and Retry-After honoring), and a typed exception hierarchy.
• Full Messages API surface: text, vision (Image blocks), tool use
  (closure / class-based with reflection-driven JSON Schema and
  automatic ToolLoop), prompt caching, extended thinking, citations.
• Streaming via Generator-based EventStream with ->toMessage()
  aggregation.
• Server-side tools: web search, computer use, bash, text editor.
• Files API and Message Batches (with JSONL streaming results and
  pollUntilDone).
• MCP connector via the mcp_servers field on Messages requests.
• Concurrent fan-out: Messages::createMany([...], concurrency: 5)
  drives N independent calls in parallel via libcurl multi-handle.
• Models listing and metadata.
• AWS Bedrock and Google Vertex AI auth providers in-package, opt-in
  via aws/aws-sdk-php / google/auth (suggested, not required).
• Test suite: 186 tests / 870 assertions, PHPStan level 9 clean,
  weekly Infection mutation testing.
• 14 runnable examples, full UPGRADING / CONTRIBUTING / SECURITY /
  CoC governance, GitHub Actions CI matrix on PHP 8.2 / 8.3 / 8.4.