PY: make fhirpy the default python client (swap simple/fhirpy examples)

[ryukzak]

Make the fhirpy async client the default for the Python examples, and move the simple requests client to its own example. Stacked on #185 (python-example-decouple), so this PR shows only the client swap.

Changes

• python-r4-us-core → fhirpy client (default). generate.ts now uses fhirpyClient: true (kept snake_case, since the profile tests depend on it). client.py/test_sdk.py use the fhirpy AsyncFHIRClient; because the models are snake_case with FHIR camelCase aliases, the client serializes with by_alias=True. The committed fhir_types/ is regenerated. Profile/offline tests are unchanged.
• python-fhirpy → simple requests client. generate.ts uses fhirpyClient: false + snake_case; it now hosts the reusable Client class (basic auth + CRUD/search) reused from python-r4-us-core's old client.

Generator fix (the interesting bit)

fhirpy's AsyncFHIRClient methods are generic over TResource, bound to a ResourceProtocol with a settable resourceType. The camelCase models satisfied this with a real resourceType field; the snake_case models expose the discriminator as resource_type (alias resourceType) and only set resourceType at runtime via a __pydantic_init_subclass__ hook — invisible to mypy. So fhirpy calls failed type-checking.

Fix in the generated FhirpyBaseModel (assets/api/writer-generator/python/fhirpy_base_model.py): declare a TYPE_CHECKING-only instance annotation

if TYPE_CHECKING:
    resourceType: str = ""

— a settable instance attr (satisfies the protocol bound + class access), defaulted (so the pydantic mypy plugin treats it as optional, not a required ctor arg), and TYPE_CHECKING-only (zero runtime change; the hook still sets the real value). ClassVar was tried first but can't satisfy a settable protocol member.

Verification

• python-r4-us-core: mypy --config-file mypy.ini . clean (42 files), 70 offline/profile tests pass, test_sdk.py (fhirpy) imports/type-checks, committed fhir_types matches a fresh generation.
• python-fhirpy: mypy --strict . clean (154 files).
• Project tsc + biome clean; python writer snapshot test green.
• Live test_sdk.py CRUD (both examples) requires Aidbox → runs in CI.

Makefile and sdk-tests.yml need no change — the targets/jobs run mypy/pytest/diff-check on whatever each example generates.

Note on naming

python-fhirpy now hosts the simple requests client (the fhirpy client moved to python-r4-us-core), so the directory name is now misleading. I left the name as-is per the request; happy to rename it (e.g. python-simple-client) as a follow-up.

[ryukzak]

Plan for these comments:

• client: "fhirpy" | "none" + deprecate fhirpyClient + fhirpy default (generate.ts:12/:30, README:21): extracted into its own API PR API: add python client option (fhirpy|none), default fhirpy; deprecate fhirpyClient #187 (it is a public-API/src change with a deprecation).
• The rest land here once API: add python client option (fhirpy|none), default fhirpy; deprecate fhirpyClient #187 + PY: consolidate python-r4 and python-us-core into python-r4-us-core #185 merge and I rebase this PR onto main:
  • drop the now-default client param from generate.ts and its README param notes;
  • rename python-fhirpy → python-r4 (path no longer means fhirpy);
  • rename the fhirpy demo client.py → demo.py (it is a runnable demo, not a Client class);
  • unwrap hard-wrapped Markdown paragraphs + add a no-wrap rule to CLAUDE.md;
  • use the generated serialize() helper in the fhirpy client instead of repeating the dump lambda.

[ryukzak]

All comments addressed (force-pushed 8fc0455):

• client API: the new client: "fhirpy" | "none" option landed in API: add python client option (fhirpy|none), default fhirpy; deprecate fhirpyClient #187; this PR now uses it — python-r4-us-core relies on the default (fhirpy, no explicit option), python-r4 sets client: "none". No example uses the deprecated fhirpyClient.
• rename path: python-fhirpy → python-r4 (it now hosts the simple requests client).
• filename: the fhirpy client.py → demo.py (it is a runnable demo, not a Client class).
• markdown: unwrapped the hard-wrapped paragraphs; added a no-wrap rule to CLAUDE.md.
• default params: removed from generate.ts and the README notes.

Verified: python-r4-us-core mypy clean + 70 offline tests + fhir_types determinism; python-r4 mypy clean (154 files); also uses the generated serialize() helper in the fhirpy client.