minor: add conformance and async lifecycle support

[manavanandani]

Summary

• enforce structured validation for initialize, step, and reset responses
• align runtime models, SDK results, JSON Schemas, and protocol validation
• preserve evaluator-visible logs and validate JSON-RPC response identifiers
• support asynchronous lifecycle hooks across stdio and Streamable HTTP
• add configurable RPC timeouts with contextual failure diagnostics
• expand automated coverage across Python 3.9 through 3.13

Why

The schemas, SDK, runtime, and conformance command previously accepted different protocol states. Async-first agent frameworks also required lifecycle hooks that could be awaited safely without breaking synchronous agents. This change establishes one enforceable, backward-compatible contract across both supported transports.

Developer impact

ecp conformance now validates method-specific contracts and supports machine-readable reports. Invalid manifests, statuses, tool calls, response identifiers, and result payloads fail with actionable diagnostics. Async @on_step and @on_reset hooks are awaited on a persistent event loop, while existing synchronous hooks remain supported.

Validation

• SDK and runtime test suites passed
• stdio and Streamable HTTP integrations passed
• flagship customer-support evaluation passed 8/8 checks
• GitHub Actions passed on Python 3.9, 3.10, 3.11, 3.12, and 3.13
• package builds, documentation build, and v0.4.0 publication completed successfully

Migration

No migration is required for valid existing agents. Malformed payloads that previously passed through are now rejected with diagnostics.