HTTP Gateway V2 drops both the multiValueHeaders and
multiValueQueryStringParameters elements.

With this change:
* Cookies passed to request and response as cookie element
  containing list of all cookie values.
* Headers with multiple values are concatenated through comma
  and passed under Headers element instead of the obsolete
  multiValueHeaders.

https://medium.com/@lancers/amazon-api-gateway-explaining-lambda-payload-version-2-0-in-http-api-24b0b4db5d36
https://aws.amazon.com/blogs/compute/building-better-apis-http-apis-now-generally-available/

Addresses issue #215.

* Fixed typing in adapter.py; Added more explicit types some places; Changed `BaseRequest.scope` to a property (formerly a method) for consistency with child classes;

* Removed `handler_kwargs`;
`api_gateway_base_path` is now an explict param;
Fixed two exception entries on lifespan config;
Added test for default `api_gateway_base_path` value;

* Fixed `AwsApiGateway` missing default for `api_gateway_base_path`;

* Added `api_gateway_base_path` param in `test_abstract_handler`;

* Removed `Optional` import from `abstract_handler`;

* Removed class attributes from `Mangum`;
Created `QueryParams` TypeAlias in `types.py`;
`api_gateway_base_path` is now a positional arg in handlers;
Fixed tests to reflect the above;
Made imports consistent to use `from`;
Cleaned up some code to make Pylance happy;
Fixed setting InitVar in `WebSocket`;

* Fixed linting error;

* Fixed coverage;

* Removed unused import;

Co-authored-by: Ramazan Elsunkaev <ramazan@up-linq.com>

* Added python3.9 and 3.10 support;
- Added python3.9 and 3.10 tests to CI;
- Added python3.9 and 3.10 classifiers to `setup.py`;
- Changed `quart` python version constraint;
- Adjusted tests to reflect the former;

* Fixed `Quart` import conditions in `test_lifespan.py`;

Co-authored-by: Ramazan Elsunkaev <ramazan@up-linq.com>

…alueHeaders (#229)

* Fix aws_api_gateway handler not accepting combined headers and multiValueHeaders

* Fix test_aws_api_gateway.py::test_aws_api_gateway_scope_basic

* Formatting

* Fix test_aws_api_gateway_scope_basic again

There was a single space where there shouldn't have been one, so the assert failed.

* More reformatting

Lines were too long

* Okay now the linters should be happy