Adds support for typing.Dict types

[ncilfone]

What does this PR do?

Added support for typing.Dict types with type checking for types of both keys and values (includes advanced types such as Dict[str, Tuple[Callable, Callable]])

Checklist

• [x] Did you adhere to PEP-8 standards?
• [x] Did you run black and isort prior to submitting your PR?
• [x] Does your PR pass all existing unit tests?
• [x] Did you add associated unit tests for any additional functionality?
• [x] Did you provide documentation (Google Docstring format) whenever possible, even for simple functions or classes?

[coveralls]

Pull Request Test Coverage Report for Build 1999629553

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 244 of 251 (97.21%) changed or added relevant lines in 12 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.6%) to 96.018%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
spock/backend/typed.py	15	16	93.75%
spock/backend/field_handlers.py	32	35	91.43%
spock/backend/utils.py	66	69	95.65%
<!--	Total:	244	251	97.21%	-->

Totals
Change from base Build 1981256000:	0.6%
Covered Lines:	1929
Relevant Lines:	2009

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💛 - Coveralls