feat: Array sum filter

[brunodccarvalho]

Implement sum filter from shopify liquid. Fixes #660 Note the last two tests assert incompatibility with the ruby version, in particular coercing of true

[coveralls]

Pull Request Test Coverage Report for Build 7261528445

Warning: This coverage report may be inaccurate.

We've detected an issue with your CI configuration that might affect the accuracy of this pull request's coverage report. To ensure accuracy in future PRs, please see these guidelines. A quick fix for this PR: rebase it; your next report should be accurate.

• 6 of 6 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.002%) to 99.468%

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Totals
Change from base Build 7033554616:	0.002%
Covered Lines:	2243
Relevant Lines:	2250

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💛 - Coveralls

[github-actions[bot]]

:tada: This PR is included in version 10.10.0 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket:

[harttle]

@all-contributors please add @brunodccarvalho for code.

[allcontributors[bot]]

@harttle

I've put up a pull request to add @brunodccarvalho! :tada: