feat: add variance function

[vibhatha]

This PR includes the addition of variance aggregation operator.

[jvanstraten]

Same as for #257: not sure how to feel about the integer variants, and the floating point operations should use float rounding options rather than integer overflow options.

[vibhatha]

Same as for #257: not sure how to feel about the integer variants, and the floating point operations should use float rounding options rather than integer overflow options.

@jvanstraten I understand. We can hold until the decision is finalized.

[jvanstraten]

YAML CI:

functions_arithmetic.yaml invalid
[
  {
    instancePath: '/aggregate_functions/4/impls/0',
    schemaPath: '#/properties/impls/items/required',
    keyword: 'required',
    params: { missingProperty: 'intermediate' },
    message: "must have required property 'intermediate'"
  }
]

@jacques-n I forgot which earlier PR this came up in. Could that have been one of the PRs you closed yesterday, maybe? I figured it'd be in main already.

[vibhatha]

@jvanstraten I updated the PR.

[jvanstraten]

LGTM aside from:

[vibhatha]

@jvanstraten updated with the suggestion.

[jvanstraten]

Same CI issues as #257, but LGTM otherwise.

[vibhatha]

@jvanstraten updated the PR, there was a typo. Let's check the CIs once again. Sorry about this.

[vibhatha]

@jvanstraten I squashed the commits to a single one. Let's see the CIs.

[jacques-n]

Hey @vibhatha , looks like other merges caused a merge conflict here. Can you rebase/fix?

Thanks!

[vibhatha]

@jacques-n shall we go with this: #257 first and I will resolve conflicts after this.

[jacques-n]

#257 is merged now.

[vibhatha]

@jacques-n could you please check the content after rebase.