Make the base instruments generic over their config type and drop the instrument bootstrap_config ignores #285

ty 0.0.87 reports invalid-mutable-override wherever a subclass narrows bootstrap_config. #284 silenced the 25 sites with per-line ignores. They fall into two groups.

Framework instruments (20 ignores)

BaseInstrument is already generic over ConfigT, but each base instrument fixes the parameter (CorsInstrument(BaseInstrument[CorsConfig])). A framework instrument then has to re-annotate the field to get its own config type:

class FastAPICorsInstrument(CorsInstrument):
    bootstrap_config: FastAPIConfig  # ty: ignore[invalid-mutable-override]

The fix is to keep the base instruments generic and let the framework instrument bind the parameter:

CorsConfigT = typing.TypeVar("CorsConfigT", bound=CorsConfig)

class CorsInstrument(BaseInstrument[CorsConfigT]): ...

class FastAPICorsInstrument(CorsInstrument[FastAPIConfig]): ...

This applies to the Cors, HealthChecks, Logging, OpenTelemetry, Prometheus and Swagger instruments. It works with slotted dataclasses, passes ty 0.0.87 without the ignore, and changes nothing at runtime. An out-of-tree subclass of CorsInstrument keeps working; ty just sees its config type as unknown until it binds the parameter.

Bootstrappers (5 ignores, out of scope)

FastAPIBootstrapper and the other four bootstrappers narrow BaseBootstrapper.bootstrap_config: BaseConfig the same way. Adding a config parameter to BaseBootstrapper breaks every one-argument subscription: BaseBootstrapper[App] raises TypeError: Too few arguments at import, including in tests/instruments/test_logging_record_filters.py.

A default (typing_extensions.TypeVar("ConfigT", bound=BaseConfig, default=BaseConfig)) keeps BaseBootstrapper[App] working on 3.11 and 3.14 (checked with typing-extensions 4.12.2 and 4.15). It would raise the typing-extensions floor from 4.6 to 4.12, though, and the stdlib only has TypeVar defaults from 3.13, so #272 couldn't drop typing-extensions after 3.11's EOL. These 5 ignores stay until 3.13 is the floor or a major release allows the break.