Birmingham | 26-ITP-May | Gabriel Pawuoi | Sprint 1 | implement sum function and tests

[KhotKeys]

Learners, PR Template

Self checklist

• I have titled my PR with Region | Cohort | FirstName LastName | Sprint | Assignment Title
• My changes meet the requirements of the task
• I have tested my changes
• My changes follow the style guide

Changelist

• Implemented the sum function that filters out non-numeric values and reduces the remaining numbers to a total.

• Added tests covering an empty array, a single number, negative numbers, decimals, mixed types, and all non-numbers.

[LonMcGregor]

See my comment on #1398

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[github-actions]

Your PR couldn't be matched to an assignment in this module.

Please check its title is in the correct format, and that you only have one PR per assignment.

If this PR is not coursework, please add the NotCoursework label (and message on Slack in #cyf-curriculum or it will probably not be noticed).

If this PR needs reviewed, please add the 'Needs Review' label to this PR after you have resolved the issues listed above.