The mypy plugin generates better types for constructors, e.g.
considering field aliases and extensible models that allow undefined
fields.

The EntraWebhookSettings() call is no longer untyped because we have the
pydantic mypy plugin installed.

We now have doctests in non-test modules.

We were requiring 3.5.0. 3.7.0 adds support for execution and trace IDs,
and I'd like to add these to the context object provided to handler
functions.

Requiring it at runtime simplifies modules using newer typing features,
as we can avoid guarding typing things with `if TYPE_CHECKING:` all the
time. This is especially beneficial when using TypeVar with default=
params, as they are not available at runtime pre-3.13, and so without
typing_extensions, we have to duplicate TypeVars using default on each
side of `if TYPE_CHECKING: ... else: ...`

We need to access it without creating an import cycle by importing
__init__ from submodules. (We could import from ucam_observe directly,
but it seems best to keep the logger source details in one place.)

The event_app_test_client_factory fixture calls into
functions_framework.create_app() via _initialize_ucam_faas_app(), so
tests using it also need to take measures to avoid functions_framework's
global state changes from leaking into other tests.

We now use cleanup_functions_framework on tests using the factory to
ensure global state changes don't leak between tests.

High-level handlers MR0: chores to prepare for new functionality

See merge request !48