[Work in progress] Request scoped construction in FastApi

[meadsteve]

fixes #180.

Usage:

# Define a contextmanager for the dependency. The __exit__ (finally in this case) will happen after the request has loaded.
@context_dependency_definition(container)
def _load_then_clean() -> Iterator[SomeThing]:
    try:
        yield SomeThing()
    finally:
        SomeThing.do_some_cleanup()

# This type then needs to be registered as a managed singleton:
deps = FastApiIntegration(
    container, request_context_singletons=[SomeThing]
)

or a context manager class:

class SomeManager:
    def __enter__(self):
        return SomeThing()

    def __exit__(self, exc_type, exc_val, exc_tb):
        pass # TODO: clean up

# Let the container now that SomeThing is managed by SomeManager
container[ContextManager[SomeThing]] = SomeManager

deps = FastApiIntegration(
    container, request_context_singletons=[SomeThing]
)

TODO:

• Implement feature using ContextManagers
• Document fastpi integration
• Document manual usage of ContextContainer.
• Add some test coverage around reusing and nesting ContextContainer
• Provide decorator context_dependency_definition that wraps @contextmanager & registers a ContextManager[X].
• Looks for ContextManager[X] first as this should be the default behaviour.
• Test that context_dependency_definition doesn't define the managed dependency by default
• Add usage of ContextContainer to the function decorators

[sourcery-ai]

Sourcery Code Quality Report

❌  Merging this PR will decrease code quality in the affected files by 0.26%.

Quality metrics	Before	After	Change
Complexity	0.47 ⭐	0.65 ⭐	0.18 👎
Method Length	25.31 ⭐	24.97 ⭐	-0.34 👍
Working memory	3.93 ⭐	3.93 ⭐	0.00
Quality	93.22% ⭐	92.96% ⭐	-0.26% 👎

Other metrics	Before	After	Change
Lines	450	573	123

Changed files	Quality Before	Quality After	Quality Change
lagom/init.py	95.04% ⭐	91.56% ⭐	-3.48% 👎
lagom/decorators.py	89.37% ⭐	90.08% ⭐	0.71% 👍
lagom/version.py	98.50% ⭐	98.50% ⭐	0.00%
lagom/integrations/fast_api.py	92.38% ⭐	89.22% ⭐	-3.16% 👎
tests/examples.py	100.00% ⭐	99.33% ⭐	-0.67% 👎
tests/test_dep_definition_functions.py	96.39% ⭐	96.32% ⭐	-0.07% 👎
tests/integrations/test_fastapi.py	90.67% ⭐	89.38% ⭐	-1.29% 👎
tests/integrations/fastapi_app/init.py	95.72% ⭐	96.03% ⭐	0.31% 👍

Here are some functions in these files that still need a tune-up:

File	Function	Complexity	Length	Working Memory	Quality	Recommendation

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