Replace pydantic with a pure dataclass-based implementation:
- Type inspection without pydantic overhead
- Schema generation using native Python types
- Custom coder system for complex type serialization
- API compatible with existing predictors

Remove multi-wheel complexity now that pydantic-based cog is replaced:
- pkg/wheels: embed only the cog wheel, remove cog-dataclass
- pkg/dockerfile: simplify wheel installation to single embedded wheel
- integration-tests: remove cog_dataclass condition
- CI: remove dataclass-specific test matrix entries
- tox: remove pydantic version matrix
- mise: consolidate coglet-python test task

Delete tests that specifically test pydantic 1.x/2.x behavior which is
no longer relevant with the dataclass-based implementation.

The dataclass implementation handles Pydantic BaseModel outputs via
duck-typing - it checks for model_dump() (v2) or dict() (v1) methods
in cog/json.py:make_encodeable(). Users can still use Pydantic for
their own model types.

Remove obsolete skips - the test uses Python 3.10 which is supported.
Verified passing with both Python and Rust coglet servers.

Remove obsolete skips - the tests use Python 3.10 which is supported.
These are slow tests that will run in CI (not -short mode).

Remove obsolete skips. This test verifies cog version in base images.
Verified passing with both Python and Rust coglet servers.

coglet_alpha is no longer a supported configuration - remove all skips.

- Simplify format_validation_error to use cog's already-formatted errors
- Remove unwrap_pydantic_serialization_iterators (no longer needed)
- Remove schema_via_fastapi fallback, use cog._schemas directly
- Update Runtime enum: remove Pydantic variant, rename NonPydantic to Cog
- Update SdkImplementation: remove Pydantic/Dataclass, use Cog/Unknown
- Update detection to check for cog._adt module
- Update comments to remove pydantic references

…BaseModel

pydantic.BaseModel outputs are no longer supported. Users should use
cog.BaseModel (a dataclass) or @DataClass for structured outputs.

Add support for user-defined healthcheck() method on predictors:
- Add Healthcheck event type to eventtypes.py
- Add get_healthcheck() helper to predictor.py
- Add healthcheck() method to Worker and _ChildWorker classes
- Add healthcheck() to PredictionRunner
- Update /health-check endpoint to call user healthcheck
- Add UNHEALTHY status to Health enum

Features:
- Sync and async healthcheck methods supported
- 5 second timeout for healthcheck execution
- Returns UNHEALTHY with error details on failure/timeout/exception

Remove [cog_dataclass] skip from healthcheck integration tests.

Add healthcheck support to coglet-rust:

Protocol:
- Add ControlRequest::Healthcheck and ControlResponse::HealthcheckResult
- Add HealthcheckStatus enum (Healthy/Unhealthy)

Orchestrator:
- Add HealthcheckResult type with healthy()/unhealthy() constructors
- Add healthcheck() method to Orchestrator trait
- Implement request/response flow via control channel
- Add semaphore to prevent concurrent healthchecks (skip if busy)
- Handle healthcheck results in event loop

HTTP:
- Add HealthResponse enum (includes transient UNHEALTHY state)
- Update /health-check to call user healthcheck when ready
- Return user_healthcheck_error in response on failure

Worker:
- Add healthcheck() to PredictHandler trait (default: healthy)
- Handle Healthcheck requests in worker event loop

Python integration (coglet-python):
- Add has_healthcheck() and is_healthcheck_async() to PythonPredictor
- Implement healthcheck_sync() with ThreadPoolExecutor + 5s timeout
- Implement healthcheck_async() with asyncio.wait_for + 5s timeout
- Wire up in PythonPredictHandler::healthcheck()

- Remove [coglet_rust] skip from existing sync healthcheck tests
- Add async healthcheck tests:
  - healthcheck_async_custom: async healthcheck returning True
  - healthcheck_async_unhealthy: async healthcheck returning False
  - healthcheck_async_exception: async healthcheck raising exception
  - healthcheck_async_timeout: async healthcheck timing out (>5s)

Python type fixes:
- _adt.py: Fix type hints for PrimitiveType methods to handle Any
- config.py: Add type arguments to dict types
- input.py: Add cast for default_factory, add type ignore for field()
- coder.py: Rename factory parameter from cls to tpe (static method)
- coders/*.py: Match renamed parameter in factory method overrides
- http.py: Add type ignores for dynamic FastAPI types and coglet module
- _inspector.py: Remove unused imports, add 'from None' to re-raises

Makefile:
- Update tox env from typecheck-pydantic2 to typecheck (pydantic removed)

Cleanup:
- Remove unused warnings import from _inspector.py
- Remove experimental coders warning

- Change timeout format from {} to {:.1} to output '5.0' instead of '5'
- Update test harness waitForServer to accept UNHEALTHY and BUSY as valid 'ready' states

- Remove pydantic from dependencies in pyproject.toml
- Simplify dependencies to minimal set
- Remove PYDANTIC_V2 constant from pyright config
- Delete cog-dataclass/ directory (was scaffold, code now in python/cog/)

- Remove unused Type import from types.py
- Remove pydantic from Go dockerfile test expectation
- Remove pydantic comment from requirements_test.go
- Fix pyright warnings in openapi_schema.py (use Any type)
- Sanitize validation error messages to first line only

Use ThreadPoolExecutor with shutdown(wait=False) to avoid blocking
when sync healthcheck exceeds timeout. Previously the context manager
would wait for the thread to complete even after timeout.