PY: type-check fixes for python-us-core example (mypy clean)

[ryukzak]

Makes mypy . on examples/python-us-core clean (0 errors). The bulk of prior noise came from a broken local mypy.ini; the genuine 18 errors are fixed here.

Slice getter raw-mode overloads

The Python profile generator emitted typed @overloads for extension getters but not for slice getters — plain slice getters declared a single flat return type yet returned the raw element object for mode="raw", so accessing raw attributes failed type checking.

Slice getters now mirror the extension pattern (Literal["raw"] → element type), and the slice element type / Literal/overload/Any imports are threaded through.

Motivation: get_systolic("raw").value_quantity no longer fails [attr-defined].

# before
def get_systolic(self, mode: str | None = None) -> Quantity | None: ...

# after
@overload
def get_systolic(self) -> Quantity | None: ...
@overload
def get_systolic(self, mode: Literal["raw"]) -> ObservationComponent | None: ...
def get_systolic(self, mode: Literal["raw"] | None = None) -> Quantity | ObservationComponent | None: ...

• Also fixes the race/ethnicity/tribal extension sub-extension getters, which had the same latent gap.
• elementTypeId is now imported explicitly for plain slices (previously compiled only because accessors happened to import the same type).

Example test cleanups

• Drop stale # type: ignore[call-arg] on raw slice getters (now type-check via overloads; the ignores never matched the real attr-defined error).
• Typed-bundle test: pass BundleEntry(resource=...) instead of dict literals — type-discriminated slices use the typed base directly, with no flat-dict form — and read entry.resource directly instead of the dead dict fallback.
• Patient equivalence test: bind identifier/name as locals and pass them directly instead of an untyped dict(...) splat (which erased value types to object).

Regenerated

• Regenerated fhir_types/ for the example.