Persistent session support

[ir4y]

• [ ] Add optinal http session parameter to the constructor
• [ ] When we do a request https://github.com/beda-software/fhir-py/blob/f00a0171099adc0d9842a97a01428ab839b78fcf/fhirpy/base/lib.py#L124 we should check if session is provided. If there is no session, the library creates a new session for this call (current behavior). When session is provided do request should use it instead of creating a new one.
• [ ] Implement attach functional and describe best practices for usage AsyncFHIRClient with aiohttp.

  class AsyncFHIRClient:
  ...
  @classmethod
  async def attach(
      cls: type["AsyncFHIRClient"], app: aiohttp.web_app.Application
  ) -> AsyncGenerator:
      session = aiohttp.ClientSession()
      client = cls(session=session)
      app[cls.key] = client
      yield
      await session.close()
  ...

app = web.Application()
app.cleanup_ctx.append(AsyncFHIRClient.attach)

• [ ] Leverage new approach at https://github.com/Aidbox/aidbox-python-sdk/blob/master/aidbox_python_sdk/main.py#L74

  def create_app(sdk: SDK):
  app = web.Application()
  app.cleanup_ctx.append(AidboxClient.attach)
  app.cleanup_ctx.append(init)
  app.update(
      settings=sdk.settings,
      sdk=sdk,
  )
  setup_routes(app)
  return app

[ruscoder]

Related #93