Support for List[Callable]

[ncilfone]

What does this PR do?

Support for List[Callable]

Checklist

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

[coveralls]

Pull Request Test Coverage Report for Build 1981195000

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

• 38 of 48 (79.17%) changed or added relevant lines in 5 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.2%) to 95.654%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
spock/backend/field_handlers.py	27	37	72.97%

Files with Coverage Reduction	New Missed Lines	%
spock/backend/field_handlers.py	1	89.47%

Totals
Change from base Build 1971124196:	-0.2%
Covered Lines:	1871
Relevant Lines:	1956

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💛 - Coveralls