Bug Fixes for v3.0.0

[ncilfone]

What does this PR do?

• Fixes bug in the new resolver when there is both a cls and self variable reference -- casts were per type but needed to be one cast post all reference resolution
• Fixed bug in new types (file and directory) for relative paths -- pathlib needs to call .resolve() prior to using the path
• Added a helper methods module -- moved the to_dict method out of the SpockBuilder and into helpers so it can be independent of having an instantiated SpockBuilder

Checklist

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

[coveralls]

Pull Request Test Coverage Report for Build 3958892498

• 36 of 36 (100.0%) changed or added relevant lines in 5 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.1%) to 95.164%

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Files with Coverage Reduction	New Missed Lines	%
spock/backend/resolvers.py	1	95.65%

Totals
Change from base Build 3939930346:	0.1%
Covered Lines:	2519
Relevant Lines:	2647

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💛 - Coveralls