feat(config): Add MeterProvider support for declarative config (#4987)

* config: add resource and propagator creation from declarative config

Implements create_resource() and create_propagator()/configure_propagator()
for the declarative file configuration. Resource creation does not read
OTEL_RESOURCE_ATTRIBUTES or run any detectors (matches Java/JS SDK behavior).
Propagator configuration always calls set_global_textmap to override Python's
default tracecontext+baggage, setting a noop CompositePropagator when no
propagator is configured.

Assisted-by: Claude Sonnet 4.6

* update changelog with PR number

Assisted-by: Claude Sonnet 4.6

* fix pylint, pyright and ruff errors in resource/propagator config

- _resource.py: refactor _coerce_attribute_value to dispatch table to
  avoid too-many-return-statements; fix short variable names k/v ->
  attr_key/attr_val; fix return type of _sdk_default_attributes to
  dict[str, str] to satisfy pyright
- _propagator.py: rename short variable names e -> exc, p -> propagator
- test_resource.py: move imports to top level; split TestCreateResource
  (25 methods) into three focused classes to satisfy too-many-public-methods
- test_propagator.py: add pylint disable for protected-access

Assisted-by: Claude Sonnet 4.6

* address review feedback: use _DEFAULT_RESOURCE, fix bool_array coercion

- replace _sdk_default_attributes() with _DEFAULT_RESOURCE from resources module
- move _coerce_bool into dispatch tables for both scalar and array bool types,
  fixing a bug where bool_array with string values like "false" would coerce
  incorrectly via plain bool() (non-empty string -> True)
- add test for bool_array with string values to cover the bug

Assisted-by: Claude Sonnet 4.6

* fix linter

* address review feedback: single coercion table, simplify attributes merge

- collapse _SCALAR_COERCIONS and _ARRAY_COERCIONS into a single _COERCIONS
  dict using an _array() factory, reducing _coerce_attribute_value to two lines
- process attributes_list before attributes so explicit attributes naturally
  overwrite list entries without needing an explicit guard

Assisted-by: Claude Sonnet 4.6

* use Callable type annotation on _array helper

Assisted-by: Claude Sonnet 4.6

* add detection infrastructure foundations for resource detectors

Adds _run_detectors() stub and _filter_attributes() to create_resource(),
providing the shared scaffolding for detector PRs to build on. Detectors
are opt-in: nothing runs unless explicitly listed under
detection_development.detectors in the config. The include/exclude
attribute filter mirrors other SDK behaviour.

Assisted-by: Claude Sonnet 4.6

* move service.name default into base resource

Merges service.name=unknown_service into base before running detectors,
so detectors (e.g. service) can override it. Previously it was added to
config_attrs and merged last, which would have silently overridden any
detector-provided service.name.

Assisted-by: Claude Sonnet 4.6

* remove unused logging import from _propagator.py

Assisted-by: Claude Sonnet 4.6

* add MeterProvider creation from declarative config

Implements create_meter_provider() and configure_meter_provider()
following the same patterns as _tracer_provider.py.

- PeriodicExportingMetricReader with explicit interval/timeout defaults
  (60s/30s) to suppress env var reading
- OTLP HTTP and gRPC metric exporters (lazy imports)
- Console metric exporter
- Temporality preference mapping (cumulative/delta/low_memory) with
  explicit dicts to suppress OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE
- Default histogram aggregation mapping with env var suppression
- View creation with selector (instrument type/name/unit/meter info)
  and stream (name/description/aggregation/attribute_keys)
- ExemplarFilter mapping; default = TraceBasedExemplarFilter (spec default)
- configure_meter_provider(None) is a no-op per spec/Java/JS behavior
- attribute_keys.excluded logs a warning (SDK View only supports inclusion)
- Pull readers raise ConfigurationError (marked _development in spec)

Assisted-by: Claude Sonnet 4.6

* add changelog entry for meter provider declarative config (#4987)

Assisted-by: Claude Sonnet 4.6

* fix linter errors

* address review feedback: simplify resource filter, propagator loading, and type annotations

Assisted-by: Claude Sonnet 4.6

* fix ruff formatting

Assisted-by: Claude Sonnet 4.6

* fix pyright: wrap EntryPoints in iter() for next() compatibility

Assisted-by: Claude Sonnet 4.6