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

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

• 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